Review Of Forensic Science: at least 1200 words and three scholarly references

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After studying this chapter you should be able to: Describe the role of the forensic pathologist

Describe the external, internal, and toxicology phases of an autopsy

Distinguish cause and manner of death

Describe common causes of death

List various categories associated with the manner of death

Describe chemical and physical changes helpful for estimating time of death

Discuss the role of the forensic anthropologist in death investigation

Describe the role of the forensic entomologist in death investigation

death investigation

algor mortis autopsy cause of death forensic anthropology forensic entomology forensic pathologist livor mortis manner of death petechiae postmortem interval

(PMI) rigor mortis

KEY TERMS

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Role of the Forensic Pathologist Few investigations bring with them the intense focus of community interest and news media cov- erage as that of a suspicious death. Generally, forensic pathologists associated with the medical examiner’s or coroner’s office are responsible for determining the cause of an undetermined or unexpected death. These officers coordinate their response with that of law enforcement in the ensuing investigation. The titles coroner and medical examiner are often used interchangeably, but there are significant differences in their job descriptions. In the United States, there’s a mix of state medical examiner systems, county medical examiner offices, and county coroner systems. The coroner is an elected official and may or may not possess a medical degree. The term coroner dates back hundreds of years to the rule of King Richard I of England (1189–1199), who created the office of the coroner to collect money and personal possessions from people who had died. The medical examiner, on the other hand, is almost always an appointed official and is usually a physician who generally is a board-certified forensic pathologist and is responsible for certifying the manner and the cause of a death.

The tasks of examining the case for the cause and manner of death and recording the results on a death certificate are the responsibilities of both offices. However, although both the coro- ner’s office and the medical examiner’s office are charged with investigating suspicious deaths, only the pathologist is trained to perform an autopsy. Ideally, the coroner or medical examiner’s office should be staffed with physicians who are board certified in forensic pathology and should charge them with determining the cause of death by autopsy. The cause-of-death determination, however, involves not just an autopsy but also the history of death, witness statements, relevant medical records, and any scene investigation, all of which constitute the surrounding circum- stances of death.

From a practical point of view, it is often not feasible for the forensic pathologist to per- sonally solicit information regarding the circumstances surrounding a death or to respond in person to every death scene. Thus, the gathering of vital information and the scene investigation can be delegated to trained coroner/medical examiner investigators who, when a crime scene is involved, coordinate their efforts with the those of crime-scene and criminal investigators. The forensic pathologist’s work is also aided by the skills of specialists including forensic anthro- pologists, forensic entomologists, and forensic odontologists.

Scene Investigation With regard to any scene investigation, protection of the overall scene and the body are of para- mount importance, as is the ultimate removal of the body in a medically acceptable manner. The death investigation involves documenting and photographing the undisturbed scene; collecting relevant physical evidence; attempting to determine time of death, which must be done in a timely fashion at the scene; and, among other things, ascertaining premortem locations of the body and whether any postmortem movement of the body occurred. Examples of observations that can be made of the body at the scene include bruises along the upper lip, which may be evi- dence of smothering; a black eye limited to the eyelids, which implies an injury from inside the head; or bleeding from the ear, which implies a basal skull fracture.

A critical phase of the death investigation will be a preliminary reconstruction of events that preceded the onset of death, so all significant details of the scene must be recorded. Blood spatter and blood flow patterns must be documented. Blood should be sampled for testing in case some of the blood was cast off by a perpetrator. Any tire marks or shoe prints must be documented. Fingerprints must be processed and collected. Of particular importance is the search for any evi- dence discarded, dropped, or cast off by a perpetrator. When a weapon is involved, there must be a concerted effort to locate and recover the suspect weapon. In the case of firearm deaths, fired bullets or casings must be found and their locations documented. In such firearm deaths, before the body is moved or clothing is removed, blood spatter directionality and trace evidence (such as hairs) on the hands must be documented. Paper bags then should be placed over the hands and secured around the wrist or arm (paper prevents moisture condensation) to preserve any ad- ditional evidence.

Photographs must always be taken before the scene is altered in any way (except from lifesaving efforts). This includes moving the body or anything on the body, such as clothing or jewelry. A particularly violent scene can carry with it a large amount of blood and disorder.

forensic pathologists Investigative personnel, typically medical examiners or coroners, who investigate the cause, man- ner, and time of death of a victim in a crime; can also be a physician who has been trained to conduct autopsies.

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Blood may be found at different locations throughout the scene. This could prove to be important in shaping the events that led to the final outcome; it may be possible to determine the initial location of the injury, as well as victim and assailant movements throughout the course of events. Initially it may be difficult to properly infer the source of the wounds and the order in which they were received at the scene. Photographs then will play a very large role when reconstructing the events later. As always, photographs should be taken with a scale, always first overall, then at medium range, then close up. The photographer must also be careful not to get caught up in cap- turing the injuries exclusively. Negative findings can also be significant. This means photographs should also be taken of areas on the body where injuries are not apparent.

Protection of the body and the overall scene is of paramount importance, as is the ultimate removal of the body in a medically acceptable manner. Often the initial phase of the investiga- tion will focus on determining the identity of the deceased, often called the decedent. Although this task may be relatively simple to accomplish through a visual examination, complications can arise. Body decomposition and the existence of extensive trauma can complicate the identi- fication. This may necessitate the application of more sophisticated technology, such as DNA, fingerprinting, dental examination, and facial reconstruction.

The Autopsy An autopsy, in its broadest definition, is simply the examination of a body after death (i.e., a postmortem examination). The autopsy can be further described as one of two types: a clinical/ hospital autopsy or a forensic/medicolegal autopsy. The clinical/hospital autopsy focuses on the internal organ findings and medical conditions. Its purpose is to confirm the clinical diagno- ses, the presence and extent of disease, any medical conditions that were overlooked, and the appropriateness and outcome of therapy. In contrast, the goal of a forensic/medicolegal autopsy is to determine the cause of death and confirm the manner of death, often to be used in crimi- nal proceedings. The forensic autopsy usually emphasizes external and internal findings while developing meaningful forensic correlations between sustained injuries and the crime scene (see Figures 5–1 and 5–2).

All the steps of the forensic autopsy must be carefully documented and photographed. The documentation should include date, time, place, by whom the autopsy was performed, and who attended the autopsy. Photographs of the injuries, complete with a scale, and descriptions of

autopsy A surgical procedure performed by a pathologist on a dead body to ascertain—from the body, organs, and bodily fluids—the cause of death.

FIGURE 5–1 An autopsy suite.

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each photograph’s location are important when correlating external wounds with internal dam- age. Negative photographs—photographs of uninjured parts of the body—are also important. The autopsy report and photographs are so important because, once the body is buried, no further evidence can be collected and no additional findings can occur.

EVIDENCE FROM THE AUTOPSY The search for physical evidence must extend beyond the crime scene to the autopsy room of a deceased victim. Here, the medical examiner or pathologist carefully examines the victim to establish the cause and manner of death. As a matter of routine, tissues and organs are retained for pathological and toxicological examination. At the same time, arrangements must be made between the examiner and investigator to secure a variety of items that may be obtainable from the body for laboratory examination. The following are among the items to be collected and sent to the forensic laboratory:

Buccal swab (for DNA typing purposes)

- ing from touching or saliva

These items of evidence should be properly packaged and labeled like all other evi- dence. Once the body is buried, efforts at obtaining these items may prove difficult or futile. Furthermore, a lengthy time delay in obtaining many of these items will diminish or destroy their forensic value.

EXTERNAL EXAMINATION The forensic autopsy consists of an external examination and an internal examination. The first steps taken for the external examination include a broad overview of the condition of the body and the clothing. Obvious damage to the clothing should be matched up to injuries on the body. General characteristics of the body should be noted, including sex, height, weight, approximate age, color of hair, and physical condition.

FIGURE 5–2 Tools used for an autopsy.

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The presence of tattoos and scars, as well as puncture and track marks, are noted. All evidence of apparent medical intervention must be carefully noted, described, and photographed because occasionally these may be misinterpreted, especially chest tube insertions and emergency cardiac punctures. The mouth and nose are examined for the presence of vomit and/or blood and trace evidence, and the ears are examined for blood. Any irritations in the nasal cavity can be indicative of drug sniffing.

Often, paper bags are placed over the hands at the crime scene until it is time to exam- ine them. This prevents contamination and possible loss of trace evidence, such as hairs and fibers. This preservation of evidence can play an important role in identifying a suspect. A victim will sometimes have skin and DNA under his or her fingernails from fighting with the assailant.

The external examination also consists of classifying the injuries. This includes distinguish- ing between different types of wounds, such as a stab wound versus a gunshot wound. The inju- ries that are examined may include abrasions, contusions, lacerations, and sharp-injury wounds. Hemorrhages in the eyelids (petechiae) are also essential to note, as they can indicate strangula- tion. Attention is also paid to the genitalia, especially in cases where sexual abuse is suspected. In these cases, vaginal, oral, and rectal samples are taken.

The discharge from a firearm will produce characteristic markings on the skin. This dis- charge is a combination of soot and gunpowder. It will leave markings called stippling or tattoo- ing around the bullet hole. The stippling can be analyzed in terms of its span and density in order to approximate the range of fire. The range of fire may prove to be the most important factor in distinguishing a homicide from a suicide.

X-ray examinations can be very useful in the autopsy process. They are most commonly performed in gunshot wound cases and stab wound cases. Even if the bullet, knife, or other piercing weapon is recovered outside the body, an X-ray will identify any fragments still inside the body. An X-ray will also help determine the path of the projectile or sharp utensil. X-rays can also be very helpful in cases where the victim was beaten, especially situations in which the victim is a child: an X-ray can show past bone fractures and a possible pattern of abuse.

INTERNAL EXAMINATION The dissection of the human body generally entails the removal of all internal organs through a Y-shaped incision beginning at the top of each shoulder and extending down to the pubic bone. Performing the internal examination entails weighing, dissecting, and sectioning each organ of the body. When required and in accordance with jurisdictional rules, microscopic examination of the sectioned organs is conducted, which can help in determining the cause of death. For example, microscopic examination of lungs and liver can confirm chronic intravenous drug abuse. Examination of the cranium requires cutting an incision from behind one ear to the other, peeling the scalp upward and backward, and sawing the skull in a circular cut; then the skull cap is removed to reveal the brain, as shown in Figure 5–3.

Special care is taken to identify any preexisting conditions or malformations in the organs that might have contributed to the death of the victim. Pulmonary edema (fluid accumulation in the lungs) is frequently found in victims of chronic cocaine and amphetamine abuse. Heart malformations may cause sus- picious death in an otherwise healthy individual.

Special attention is paid to the digestive tract if poison- ing is suspected. The stomach can show partially digested or dissolved pills. Chemical analyses can also be carried out to show signs of poisoning. The amount of pills or tablets in the stomach can aid in the determination of manner of death as well. It is not always a sure sign, but typically it is unlikely that a person will accidentally swallow a large number of pills. This would suggest suicide rather than an accidental overdose. Stomach contents may reveal the deceased’s last meal. The extent of digestion can help with determining the time of death.

FIGURE 5–3 A brain during autopsy.

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TOXICOLOGY The internal examination is also where toxicological specimens are taken. These include samples of blood, stomach content, bile, and urine. All bile in the gallbladder and all stomach content are collected. In addition to these, brain matter, liver, and vitreous humor are also gathered. These specimens can play especially large roles in cases where poisoning or drug abuse is suspected.

Blood is often tested to determine the presence and levels of alcohol and drugs. Blood should be taken from areas of the body where there is the least chance of contamination. Blood should never be collected from body cavities, where it may be contaminated from adjacent structures. Many changes occur in the body after death, and these changes can alter the drugs present in the system at the time of death. This can make interpreting how much of a drug was present, if any at all, a very challenging task. Some drugs redistribute or reenter the blood after death and thus may complicate the interpretation of postmortem blood levels of these drugs. This phenomenon is known as postmortem redistribution. For this reason, it is best to collect blood at distant areas of the body to allow the toxicologist to compare the agreement of the drug concentrations found. The ideal location to retrieve the blood is internally, directly from the inferior vena cava (the large vein inside the lower abdominal region, which receives its blood from the femoral veins) using a syringe. Where postmortem redistribution of drugs may have occurred, blood should also be collected at autopsy from the superior venous system directly above the heart.

For illicit as well as legal substances, it is necessary to know what levels are indicative of therapeutic use and what levels indicate toxicity of a given substance. Much information regard- ing therapeutic versus toxic drug levels has been published. This data can help pathologists and toxicologists ascertain the cause of death. Most drug-related deaths are quite apparent from the blood concentrations of alcohol and/or a drug found in the postmortem toxicological report. (Note that depressant drugs will act in concert with alcohol.) However, in some cases of drug- induced death, drug levels may not always provide evidence. Cocaine is a prime example of this. Cocaine-induced sudden death is an event with an incubation period. Structural alterations of the cardiovascular system are required, and such alterations take months, or perhaps years, of chronic cocaine use. In these individuals, death and toxicity may occur after the use of even a trivial amount of the drug.

Unlike drug analyses, general testing for poisons is not a routine procedure carried out by the pathologist. However, if a specific poison is suspected, a particular test must be performed. A body that displays a cherry-red discoloration often leads a pathologist to suspect carbon monoxide poisoning. The pathologist would then perform a toxicological test of the blood. Poisoning by cyanide could also produce a pinkish discoloration. Often, cyanide toxicity will show additional signs, such as a distinct smell of burnt almonds. Corrosion around the lips of a victim may lead to a suspicion of ingesting an acid or alkaline substance.

Cause of Death A primary objective of the autopsy is to determine the cause of death. The cause of death is that which initiates the series of events ending in death. The most important determination in a violent death is the character of the injury that started the chain of events that resulted in death. However, if the sequence of events leading to death is sufficiently prolonged, then the decedent may actu- ally suffer from adverse medical conditions brought about by the initial injury and then die as a result of those conditions. In that case, it will be up to the forensic pathologist to determine that the original injury inflicted on the victim was the underlying cause of death. Some of the more common causes of death are discussed here.

BLUNT-FORCE INJURY A blunt-force injury is caused by a nonsharpened object such a bat or pipe. A blunt-force injury can abrade, or scrape, tissue. If tissue is crushed by a blunt force to the point of causing skin to overstretch, a laceration will form, characterized by the skin splitting and tearing. Lacerations exhibit abrasions around the open wound, tissue bridging within the open wound, and torn or disturbed tissue beneath the skin surrounding the open portion of the wound. Blunt-force injury can also crush tissue. This will cause bleeding from tiny ruptured blood vessels within and beneath the skin, known as a contusion, or bruise (see Figure 5–4). Much has been written about determining the age of bruises, but forensic pathologists have become keenly aware that attempting to “age” bruises based on color and changes in color over time is fraught with

WEBEXTRA 5.1 See How an Autopsy Is Performed

cause of death Identifies the injury or disease that led to the chain of events resulting in death.

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difficulty, and contusions must be interpreted with great care and reserve. Some contusions only become visible externally over time, and frequently, bruises will not be visible externally but become eminently visible internally within soft tissues (e.g., in the abdomen and on the back, arms, and legs).

A contusion can sometimes exhibit the pattern of the weapon used. For ex- ample, if a person wearing a ring strikes another person, the ring may imprint its pattern onto the skin. A person who stomps on another may leave the impression of his or her shoe heel. Over time, however, the bruise will lose its original shape and pattern and undergo color changes. Some objects will produce a characteris- tic bruised perimeter and a white center.

The outward appearance of the injuries does not always coincide with the injuries sustained inside the body. This is something the pathologist must keep in mind when examining blunt-force injuries. A single blow to certain parts of the body can cause instantaneous death with little visible damage. Likewise, a blow to the head can cause a concussion that can be instantly fatal.

SHARP-FORCE INJURIES Sharp-force injuries occur from weapons with sharp edges, such as knives or blades. These weapons are capable of cutting or stabbing. A cut is formed when the weapon produces an injury that is longer than it is deep. In contrast, a stab is deeper than its length. As shown in Figure 5–5, the tissue associated with these types of wounds is not crushed or torn but sliced.

A scene that involves a sharp-force injury is usually especially bloody and unruly. Blood may be found at different locations throughout the scene. Again, this information may make it possible to determine the initial location of the injury as well as where the body was moved throughout the course of events. Particularly important in sharp-force cases is to examine the victim for defensive wounds. A victim’s forearm that exhibits wounds may indicate defense wounds. These occur when the victim attempts to fight off the attacker or block assaults. Though defense wounds are more typical on the outer fore- arms, they can also be evident on the lower extremities if the victim tries to protect himself or herself by kicking. A lack of any defense wounds can lead a pathologist to conclude that the victim was either unconscious or somehow tied up during the assault.

ASPHYXIA Asphyxia encompasses a variety of conditions that involve interference with the intake of oxygen. For example, death at a fire scene is caused primarily by the extremely toxic gas carbon monoxide. When carbon monoxide is present, hemoglobin, the protein in red blood cells that transports oxygen, will bind to the carbon monoxide instead of oxygen. This is carbon monoxide poisoning, and this deadly complex of hemoglobin and carbon monoxide is known as carboxyhemoglobin. Bound up with carbon monoxide, the hemoglobin is prevented from transporting oxygen throughout the body, causing asphyxia. High levels of carbon monoxide in the blood will cause death. Low levels of carbon monoxide can cause a victim to become disoriented and lose consciousness.

Carbon monoxide will not continue to build up in the body after death. The levels found in a fire victim then can be used to determine whether the individual was breathing at the time of the fire. The presence of soot is an- other indicator that the victim was alive during the fire. These black particles are often seen in the airway of fire victims who inhaled smoke before death. During the autopsy, soot can be observed, especially in the larynx and trachea and even in the lungs. Sometimes the victim will actually swallow the soot. In these cases, traces can be found in the esophagus and the lining of the stomach.

The ultimate cause of a death from hanging is typically the cessation of -

chiae on the eyelids, along with a swollen and a blue/purplish appearance of

FIGURE 5–5 A stab wound.

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FIGURE 5–4 Bruising (contusions) on the skin.

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the face. Petechiae are very small and are caused by blood having escaped into the tissues as a result of capillaries bursting (see Figure 5–6). Although petechiae are witnessed in hanging cases, they are more common in strangulation deaths. Typically the hyoid bone (the bone on which the tongue rests) and thyroid cartilage (located below the hyoid) are not fractured in cases of hanging. A break of the thyroid cartilage is common, however, in manual strangulation cases.

In hangings it is vitally important to document exactly how the victim was initially found and the position of the encircling noose, as shown in Fig- ure 5–7. The type of knot used may strongly support the notion that another person was involved in the hanging. This means that the knot should always be preserved for later examination. Either the noose should be slipped off the victim’s head intact, or the noose should be cut distant from the knot. Defense wounds are common on strangulation victims. Often the marks found on the neck of a victim are the victim’s own, made in the attempt to loosen whatever was constricting his or her neck. Even in cases of hanging by suicide, there can be defensive wounds on the neck.

Smothering can occur by various materials that block the mouth, nose, and internal airway. Pillows or a hand can inhibit breathing. Gags that are used to silence a victim can be sucked into the airway and block oxygen flow. Typically a death by smothering is homicidal in nature. Accidental smother- ing usually occurs only in infants or in cases where a victim is trapped under an obstruction.

GUNSHOT WOUNDS When evaluating a gunshot wound, the estimated range of fire is one of the most important characteristics to analyze (see Figure 5–8). The appearance of the wound can help in estimating whether the firearm used to inflict the wound was discharged while in contact with the victim’s body or from a distance of only inches to many feet away (see Figure 5–9). The investigator will compare powder residue distribution around the wound to test fires collected from the inflicting firearm to make this estimate. Obviously if the firearm was fired at a distance of several feet, suicide is a highly unlikely cause of death because the wound could not have been self- inflicted. Gunpowder residue on the victim’s is a possible indicator of suicide, but this is not always the case. Evidence of contact shots, that is, shots fired with the gun held against the body of the victim, typically indicates that the death was not an accident. The autopsy must include a determination of the path or “wound track” of the projectile. The wound track is determined by observing the wound from the outside of the body, following the track of the projectile through the body, and documenting its terminus. The pathologist will recover any and all projectiles from the body, carefully protecting the forensic markings. The autopsy of gunshot victims should include several facts in addition to the general autopsy facts; scene investigation and the results of toxicological and serological analyses are important. All findings regarding the bullet wounds should be noted, as well as descriptions of the clothing. The police report with a thorough description of the scene is also important.

A gunshot wound may not necessarily explain why a victim died. A person who sustains a gunshot wound can bleed to death in a matter of minutes or up

to several hours. Infection can also be a contributory cause of death, especially in cases where the victim was shot in the abdomen; he or she might live several days but eventually succumb to infection. In cases where the victim was shot in the head but survives in a comatose state, pneu- monia often develops. These intervening factors are considered contributory causes of death, but the gunshot wound is still considered the underlying cause of death.

SUBSTANCE ABUSE Drug abuse continues to be an enormous problem in the United States. Drug enforcement is a multibillion-dollar industry. Many of the abused drugs in the country are illegal, but not all are. Deaths as a result of substance abuse are common cases that a forensic pathologist must face. Because drug abuse is so common, the forensic pathologist will routinely test for the presence of drugs in nearly all investigations, and routine tests are available for many commonly abused drugs. As technology has improved, many drugs can be detected at very

petechiae Pinpoint hemorrhaging often observed in the white area of the victim’s eyes; often observed in strangulation cases.

FIGURE 5–7 A ligature pattern on a neck with corresponding ligature.

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FIGURE 5–6 Petechial hemorrhages in a victim’s eye.

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low levels. These factors have helped considerably in making substance abuse testing easier and less expensive.

Drug abuse can directly cause death, or it can cause complications that can serve as a contributing factor to death. An abuser can misuse a drug or a number of drugs for years, accumulating detrimental effects in that time. Death as a result of those effects is typically labeled a natural death by the pathologist. Drugs can also alter a person’s judgment and psychomotor skills to the point that a fatal accident occurs. Drugs are also often at the source of acts of violence that result in death.

Manner of Death The manner of death relates to the circumstances that led to the fatal result and is the culmination of the complete investigation, including the determi- nation of cause of death. The certification of the circumstances and man- ner of death is the responsibility of the coroner’s and medical examiner’s offices. The manner in which death occurred is classified in death certifica- tions as one of five categories: homicide, suicide, accidental, natural, or undetermined.

HOMICIDE Although there is no universal agreement on its definition, generally the term homicide, as certified by coroners’ and medical examiners’ offices, is defined as a nonaccidental death resulting from grossly negligent, reckless, or intentional actions of another person. Both the cause and manner of death, as certified by the coroner’s/medical examiner’s offices, can become the subject of expert debate during any subsequent judicial proceedings. However, this does not result in a revision of the death certification unless there has been negligence on the part of the certifying offices.

If the pathologist was unable to go to the scene, he or she should receive adequate information detailing the conditions of the scene from coroner/medical examiner investigators and law enforcement personnel. This information should include how the body was discovered as well as when and where. It is also an important first step for investigators to make note of the algor mortis, livor mor- tis, and/or rigor mortis of the body at the scene. These will help determine time of death.

SUICIDE Suicide is the result of an individual taking his or her own life with lethal intention. For a determination of suicide, it must be demonstrated that the individual carried out the act alone. If there is any doubt about the intentions of the victim, the death is not classified as a suicide; the death is ruled as an accident or even as undetermined. The most common methods of suicide include self-inflicted gunshot wounds, hanging, and drug overdosing. Although drug abuse is deliberately committed by a victim, it is not considered suicide unless it was clearly intended as a lethal act.

homicide. The victim’s personal history, including his or her psychiatric history, becomes rel- evant. Suicidal threats or past attempts would give obvious evidence of a suicide as opposed to an accident. In all cases of suspected suicide, a thorough search of the victim’s possessions should be made to locate a suicide note.

Multiple gunshot wounds might lead one to suspect homicide. However, a person who is committed to ending his or her own life may take several shots if the wounds are not instantly fatal. It is imperative to confirm that it is physically possible that the victim could inflict the wounds. There are a few areas of the body that strongly point toward homicide. These are areas that are not easily accessible to the victim’s own reach. For example, anywhere on the back of a victim is difficult and sometimes impossible for the victim to have shot by his or her own hand. This is especially true if the wound was made in the back of the head. For suicides, the most common shot is to the temple of the head. The mouth, forehead, and chest are also common.

FIGURE 5–9 A gunshot entrance wound to the head from a weapon fired several inches from the target.

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FIGURE 5–8 A contact gunshot wound to the temple of a suicide victim.

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to manner of death A determination made by a forensic pathologist of the cause of death. Five broad categories are homicide, suicide, accidental, natural, and undetermined.

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Also, if the wound was immediately incapacitating, the weapon should be present. Blood spatter analysis should be consistent with the proposed order of events. All victims involved in gunshot cases should have their hands swabbed for gunshot residue.

ACCIDENTAL In all deaths that are ruled accidental, there must not be intent to cause harm through gross negligence on the part of a perpetrator or the victim. Traffic accidents make up a large percentage of accidental deaths, followed by drug overdoses and drownings. The surviving driver may have vehicular homicide charges brought against him or her, especially if the driver is determined to have been driving under the influence of drugs or alcohol. In this case, the official manner of death certified on the death certificate in many jurisdictions would be vehicular homicide.

All cases that have the possibility of being a ruled an accident should have toxicological analyses carried out. The presence of drugs and/or alcohol in the victim’s system can poten- tially affect the determination. Also, the pathologist should be aware that some events might be disguised as accidents to cover up a homicide or suicide. For example, bodies recovered from a house fire might show evidence that the victims were dead before the fire started. This evidence might include a lack of soot in the victims’ airways or no indication of elevated levels of carbon monoxide. This scenario, although not common, illustrates how the autopsy and scene can appar- ently not correlate with each other. No matter how obvious a scene may appear, the two should always correspond with one another. Cases of electrocution are generally ruled as accidents, but this may be difficult to prove. High-voltage electrocutions will usually leave burns on the body. Low-voltage electrocutions, however, may show few or no signs of trauma. The scene then be- comes crucial in ascertaining the events surrounding the death.

The determination of manner of death in drownings (accidental, suicidal, or homicidal), falls (accidental, pushed, or deliberate), and asphyxiations can be exceedingly difficult, and therefore the investigation into all of its components becomes much more important than the autopsy.

NATURAL CAUSES The differentiation between the categories of manner of death can be difficult to make. The distinction between natural and accidental deaths can pose challenges. The classification of natural death includes disease and continual environmental abuse. This abuse can encompass various events, such as chronic drug and alcohol abuse or longtime exposure to natural toxins or asbestos. Again, although drug abuse is deliberately committed by the victim, a death caused by drug use is not considered suicide unless it is clear that drugs were taken as an intentionally lethal act. Acute ethanol intoxication can be ruled as either natural or accidental depending on the circumstances. If the victim suffers from chronic alcoholism, the death is ruled to be natural. If the victim is a teenager experimenting with alcohol for the first time, the death is ruled an accident.

UNDETERMINED A death is ruled to be undetermined only when a rational classification cannot be established. This can happen when the mechanism that caused the death cannot be determined by a physical finding at the autopsy or because of the absence of meaningful findings in the subsequent toxicological and microscopic examinations.

Estimating Time of Death A pathologist can never give an exact time of death. However, there are many characteristics that the examiner can analyze in order to arrive at an approximate time of death. Some features can give a very probable time of death, but others are extremely variable. Witnesses can serve to reconstruct the events leading up to the death and the incidents that occurred after the death, along with the times when they occurred, but a single witness’s account alone is not enough to make an accurate determination. The chemical and physical changes that occur after death must also be examined.

ALGOR MORTIS After death the body undergoes a process in which it continually adjusts to equalize with the environmental temperature. This process is known as algor mortis. An algor mortis determination must be performed at the scene as early as possible. The first step is to determine as best as possible what the environmental temperatures may have been prior to discovering the body. Then the environmental temperature and the bilateral axillary and/or ear canal temperatures are recorded at the crime scene (rectal temperatures are usually too disruptive

algor mortis A process that occurs after death in which the body temperature con- tinually cools until it reaches the ambient or room temperature.

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at the scene). The cooling rate of a typical body can be used to estimate the time of death. At average ambient temperatures of 70–72°F, the body loses heat at a rate of approximately of 1–1.5°F per hour until the body reaches the ambient or room temperature. However, the rate of heat loss is influenced by factors such as ambient temperature, the size of the body, and the victim’s clothing. Because of such factors, this method can only approximate the amount of time that has elapsed since death.

LIVOR MORTIS Another condition that begins when circulation ceases is livor mortis. When the human heart stops pumping, the blood begins to settle in the parts of the body closest to the ground. As shown in Figure 5–10, the skin becomes a bluish-purple color in these areas. The onset of this condition begins 20 minutes to 3 hours after death and under average conditions continues for up to 16 hours after death, at which point all lividity, or coloring, is fixed. Initially, lividity can be pressed out of the vessels when the skin is pressed, that is, lividity can be “blanched.” With time, coloring becomes “fixed” in the vessels, beginning in the most dependent (lowest) areas and progressing to the least dependent areas, and then finally no blanching can be elicited anywhere. In any case, levels of lividity are tested at the scene with regard to whether it is completely fixed, blanches when subjected to light pressure, or blanches when subjected to significant pressure. A range of time of death can be estimated if at least some of the lividity is still blanching. However, the environmental temperature and the rate of body temperature decline (i.e., algor mortis) directly affect the rate of fixation of lividity and therefore must be taken into account when attempting to estimate time of death from lividity.

Different lividity patterns in a body may indicate that the body was moved after death but before livor mortis had fully fixed. The skin does not become discolored in areas where the body is restricted by either clothing or an ob- ject pressing against the body. This information can be useful in determining whether the victim’s position was changed after death. Livor that is a deep purple is often seen in cases where the victim suffered asphyxia or heart failure.

RIGOR MORTIS Immediately following death, a chemical change occurs in the muscles that causes them to become rigid, as shown in Figure 5–11. This condition, rigor mortis, evolves over the first 24 hours under average temperature and body conditions. This rigidity subsides as time goes on, however, and disappears after about 36 hours under average conditions. Rigor will develop in the position that the body was in at the time of death, essentially

FIGURE 5–10 Livor mortis.

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livor mortis A medical condition that occurs after death and results in the set- tling of blood in areas of the body closest to the ground.

FIGURE 5–11 Rigor mortis in the arm of a decedent.

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rigor mortis A medical condition that occurs after death and results in the stiff- ening of muscle mass. The rigidity of the body begins within 24 hours of death and disappears within 36 hours of death.

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freezing the body in that pose. Discovering a body in a position that defies gravity is a likely indicator that the body was moved after death.

Although rigor mortis can roughly indicate a time of death, there are factors that can alter this determination. An environment that is hot can speed up the process significantly. Conditions that affected the body before death, such as exercise or physical activity, can also speed up the process. Because rigor mortis occurs as a result of the muscles stiffening, individuals with de- creased muscle mass may not develop rigor completely. Examples of these individuals may be infants or elderly or obese persons.

POTASSIUM EYE LEVELS Another approach helpful for estimating the time of death is to determine potassium levels in the decedent’s ocular fluid, that is, the fluid within the eye, also known as the vitreous humor. It is important to draw a clean, bloodless vitreous sample from one eye with a syringe as soon as possible at the scene, then draw a second sample from the other eye an hour or two later. After death, cells within the inner surface of the eyeball release potassium into the ocular fluid. By analyzing the amount of potassium present at various intervals after death, the forensic pathologist can determine the rate at which potassium is released into the vitreous humor and use it to approximate the time of death. However, the rate of potassium release also is dependent on ambient temperatures.

STOMACH CONTENTS Special attention must be paid to the digestive tract. The identification of food items in the stomach may help determine the location of the decedent prior to death (during his or her last meal). The quantity, consistency, and color of bile, and the degree of digestion of food in the stomach and its passage into the small intestine can help determine the time of death. The stomach also can contain partially digested or dissolved pills. Chemical analyses can be carried out to identify and analyze substances found in the stomach. These can aid in the determination of cause and manner of death.

DECOMPOSITION Once decomposition has set in, the preceding methods of determining time of death are no longer of any use. After death, two decomposition processes take place: autolysis and putrefaction. Autolysis is fundamentally self-digestion by cells’ own enzymes, and its rate varies from organ to organ depending on the mechanism of death, the enzyme content of the respective organs, the position of the body, and environmental factors. Putrefaction is decomposition carried out by microorganisms such as bacteria. Putrefaction is accompanied by bloating, discoloration, and a foul smell caused by accumulating gases. Again, the rate of putrefaction is dependent on the mechanism of death (for example, congestive respiratory versus sudden cardiac death) allowing bacteria to spread from the bowel, presence or absence of infection, environmental temperatures and humidity, degree of obesity, extent of clothing, and so on. Green discoloration often begins in the abdomen. Darker green or purple discoloration follows on the face. The skin begins to blister with gas and then peel (called slippage). The skin of the hands and feet can actually detach and come off the body like a glove. This stage is also accompanied by bloating, which causes the eyes to bulge and the tongue to protrude. The chest and extremities will then turn a green/purple discoloration and bloat.

In the postmortem period of decomposition, a waxy substance called adipocere may form. Adipocere adds a white or gray waxlike consistency to fatty tissues in the face and extremities that can take on a yellow to tan color. Typically, adipocere takes about three months to develop.

Role of the Forensic Anthropologist Forensic anthropology is concerned primarily with the identification and examination of hu- man skeletal remains. Skeletal bones are remarkably durable and undergo an extremely slow breakdown process that lasts decades or centuries. Because of their resistance to decomposition, skeletal remains can provide a multitude of individual characteristics long after a victim’s death. An examination of bones may reveal a victim’s sex, approximate age, race, height, and the nature of a physical injury.

Recovering and Processing Remains Thorough documentation is required throughout the processes of recovery and examination of human remains. A site where human remains are found must be treated as a crime scene (see

forensic anthropology The use of anthropological knowl- edge of humans and skeletal structure to examine and identify human skeletal remains.

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Figure 5–12). These sites are usually located by civilians who then contact law enforcement personnel. The scene should be secured as soon as possible to prevent any further alteration of the scene. The scene should then be searched to locate all bones, if they are scattered, and any other items of evidence such as footwear impressions or discarded items. Many tools can be useful when searching for evidence at a “tomb” site, including aerial photography, metal detectors, ground-penetrating radar, infrared photography, apparatuses that detect the gases produced by biological decomposition, and so-called cadaver dogs that detect the odors caused by biological decomposition. All items that are found must be tagged, photographed, sketched, and documented in notes. Once all bones and other evidence are found, a scene sketch should be made to show the exact location of each item (preferably using Global Po- sitioning System [GPS] coordinates) and the spatial relationship of all evidence. Once the skeletal remains have been recovered, they can be examined to deduce information about the identity of the decedent.

Determining Victim Characteristics The sex of the decedent can be determined by the size and shape of various skeletal features, especially those of the pelvis and skull, or cranium. Female pelvic bones tend to form a wider, more circular opening than that in a male pelvis because of a woman’s child-bearing capabili- ties. The female sacrum (flat bone above the tailbone) is wider and shorter (see Figure 5–13[a]) than a male’s; the length and width of the male sacrum are roughly equal (see Figure 5–13[b]). The angle formed at the bottom of the pelvis (i.e., subpubic angle) is approximately a right angle (90 degrees) in females, but it is acute (less than 90 degrees) in males. In general, male craniums are larger in overall size than those of females. A male cranium tends to have a more pronounced brow bone and mastoid process (a bony protrusion behind the jaw) than a female cranium (see Figure 5–14). See Table 5–1 for a summary of the differing features of female and male skeletons from head to toe. These are typical cases; not all skeletons may display the given characteristics to clearly indicate the sex of the decedent.

The method for determining the age of a decedent varies depending on the victim’s growth stage. For infants and toddlers, age can be estimated by the length of the long bones (e.g., femur and humerus) when compared to a known growth curve. Different sections of the skull also fuse

FIGURE 5–12 Crime-scene site showing a pelvis partly buried in sand and a femur lying across a revolver.

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together at different stages during early development, and the appearance of fused or divided sec- tions can be used to estimate the age of bones still in early developmental stages (see Figure 5–15). In infant skeletons, formation of teeth can be used in age determination; this is based on the fact that permanent teeth start to form at birth. If the skeletal remains belong to a child, the age of the decedent may be determined by observing the fusion or lack of fusion of epiphyseal regions of bones such as those of the mandible (i.e., lower jaw), fingers, wrist, long bones, and clavicle

FIGURE 5–13 (a) Frontal shot of female pelvis and hips. This view shows the wide, circular nature of the pelvic opening and the short, wide nature of the sacrum. (b) Human male pelvis. This view shows the narrow pelvic opening and long, narrow sacrum.

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FIGURE 5–14 Male (left) and female (right) human skulls showing male skull’s larger size and more pronounced brow bone.

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(see Figure 5–16). The average age at which each of these regions fuses is known and can be compared against the state of the remains to provide a range of possible ages for the decedent. A child’s cranium may also be identified by its smaller size and the presence of developing teeth as contrasted with the skull of an adult showing developing teeth (see Figure 5–17). After age 21, age is estimated by the level of change the surfaces of the bones have undergone, especially in areas of common wear such as the pubic symphysis. The pubic symphyseal face shown in Figure 5–18 is a raised platform that slowly changes over the years from a rough, rugged surface to a smooth, well-defined area. See Table 5–2 for a summary of the skeletal closures by age. It is important to note that these are average ages for closures; not all skeletons display closures at the given ages.

TABLE 5–1 Summary of Skeletal Features by Gender

Female Male

Cranium (skull) Medium to large in size Large in size Forehead High in height, vaulted, rounded Low in height, sloped, backward Brow bone Diminished Pronounced Mastoid process Diminished or absent Pronounced Mandible (jaw) angle

Obtuse (.90 degrees) Approximately right (90 degrees)

Pelvis opening Wide, circular Narrow, noncircular Sacrum Short, wide, turned outward Approximately equal width/

length, turned inward Subpubic angle Approximately right (90 degrees) Acute (,90 degrees) Femur Narrow, angled inward from

pelvis Thick, relatively straight from pelvis

Overall skeleton Slender Robust

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FIGURE 5–15 A lateral view of a fetal skull showing the separated bones of the skull before they have had a chance to fuse.

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Although the categorization “race” has come under scrutiny and is difficult to define, forensic anthropologists use broad classes to characterize the likely (but not definite) ancestry of skeletal remains. The possible racial ancestry of the dece- dent can be assessed by the appearance of various cranial features on the skeletal remains. For example, eye orbits tend to be circular in Mongoloid skeletons (i.e., of Asian descent), oval in Caucasoid skeletons (i.e., of European descent), and square in Negroid skeletons (i.e., of African descent). The frontal plane of the cranium may also vary. The frontal plane of Mongoloid craniums may be flat or projected outward, that of Caucasoid craniums is flat, and that of Negroid craniums is projected outward. The nasal cavity tends to be small and rounded in Mongoloids, long and narrow in Caucasoids, and wide in Negroids. Skeletal remains of decedents of Asian ancestry, including those of Native American descent, also tend to have “scooped-out” or shovel-shaped incisor teeth. See Table 5–3 for a summary of the differing features of skeletons that can indicate ancestry. These are typical cases; not all skeletons may display the given characteristics to indicate the ancestry of the decedent.

The height of the victim when alive can be estimated by measuring the long bones of the skeleton, especially in the lower limbs. Even partial bones can yield useful re- sults. However, meaningful stature calculations from known equations must be based on the determined sex and race of the remains. See Table 5–4 for examples of equations used to calculate the height of the decedent from skeletal remains. These equations should yield estimations within 5 cm of actual height.

Other Contributions of Forensic Anthropology A forensic anthropologist may create facial reconstructions to help identify skeletal remains. Facial reconstruction clay is placed and shaped over the victim’s actual cranium, and it takes into account the decedent’s estimated age, ancestry, and sex (see Figure 5–19). With the help of

FIGURE 5–16 Colored X-rays of healthy human hands at 3 years (left) and at 20 years. Bones display in red, and flesh is in blue. The child’s hand has areas of cartilage in the joints between the finger bones (i.e., epiphyseal areas), where bone growth and fusion will occur. In the adult hand, all the bones are present, and the joints have closed.

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FIGURE 5–17 The skull of an adult, with part of the jaw cut away to show the developing teeth.

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FIGURE 5–18 The symphysis pubis shown magnified beneath human pelvic bones.

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TABLE 5–2 Summary of Skeletal Closures by Age

Age (months) Closure

6–9 Mandible (jaw) fused 4–6 Humerus head bones fused 7–8 Pelvis frontal bones fused 4–16 Femur shaft sections built 9–13 Elbow bones fused 10 Finger bones fused 16–18 Femur head bones fused to shaft bones 18 Wrist bones fused 18–21 Humerus head bones fused to shaft bones 18–24 Sternum fused to clavicle 20–25 Pelvic bones fully formed 21–22 Clavicle fused 21–30 Labodial suture (rear of cranium) fused 24–30 Sacrum bones fused 30–32 Sagittal suture (center of cranium) fused 48–50 Coronal suture (front of cranium) fused

TABLE 5–3 Summary of Skeletal Characteristics Indicating Racial Ancestry

Eye Orbitals Nasal Cavity Incisors Cranium Frontal Plane

Caucasoid Oval Long, narrow Smooth Flat Mongoloid Circular Small, rounded Shoveled

interior Flat or projected outward

Negroid Square Wide Smooth Projected outward

TABLE 5–4 Equations for Height Calculation from Skeletal Remains

Caucasoid Negroid Unknown Ancestry

Female Height (cm) 5 femur length (cm) 3 2.47 1 54.10

Height (cm) 5 femur length (cm) 3 2.28 1 59.76

Height (cm) 5 femur length (cm) 3 3.01 1 32.52

Height (cm) 5 humerus length (cm) 3 3.36 1 57.97

Height (cm) 5 humerus length (cm) 3 3.08 1 64.67

Height (cm) 5 humerus length (cm) 3 4.62 1 19.00

Male Height (cm) 5 femur length (cm) 3 2.32 1 65.53

Height (cm) 5 femur length (cm) 3 2.10 1 72.22

Height (cm) 5 femur length (cm) 3 2.71 1 45.86

Height (cm) 5 humerus length (cm) 3 2.89 1 78.10

Height (cm) 5 humerus length (cm) 3 2.88 1 75.48

Height (cm) 5 humerus length (cm) 3 4.62 1 19.00

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FIGURE 5–19 Trooper Sarah Foster, a Michigan State Police forensic artist, works on a three-dimensional facial reconstruction from an unidentified human skull at Richmond Post in Richmond, MI.

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Identifying a Serial Killer’s Victims The worst serial killer in the United States calmly admitted his guilt as he led investigators to a crawl space under his house. There, John Wayne Gacy had buried 28 young men, after bru- tally raping and murdering them in cold blood. Because no forms of identification were found with the bodies, the police were forced to examine missing-person reports for leads. How- ever, these boys and men were so alike in age, race, and stature that police were unable to individually identify most of the vic- tims. Clyde Snow, the world-renowned forensic anthropologist from Oklahoma, was asked to help the investigators make these difficult identifications.

Snow began by making a 35-point examination of each skull for comparison to known individuals. By examining each skeleton, he made sure each bone was correctly attributed to an individual. This was crucial to later efforts because some of the victims had been buried on top of older graves, mingling their remains. Once Snow was sure all the bones were sorted properly, he began his in-depth study. Long bones such as the femur (thigh bone) were used to estimate each individual’s

height. This helped narrow the search in the attempt to match the victims with the descriptions of missing people.

After narrowing the list of missing people to those fitting the general description, investigators consulted missing per- sons’ hospital and dental records. Evidence of injury, illness, or surgery and other unique skeletal defects of the victims were matched to information in the records to make identifications. Snow also pointed out features that gave useful clues to the victim’s behavior and medical history. For example, he discov- ered that one of Gacy’s victims had a healed fracture on his left arm, and that his left scapula (shoulder blade) and arm bore the telltale signs of a left-handed individual. These details were matched to a missing-person report, and another young victim was identified.

For the most difficult cases, Snow called in the help of forensic sculptor and facial reconstructionist Betty Pat Gatliff. She used clay and depth markers to put the “flesh” back on the faces of these forgotten boys in the hopes that someone would recognize them after the photographs of the reconstructed faces were released to the media. Her efforts were successful, but investigators found some families unwilling to accept the idea that their loved one was among Gacy’s victims. Even with Gatliff’s help, nine of Gacy’s victims remain unidentified.

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this technique, a composite of the victim can be drawn and advertised in an attempt to identify the victim.

Forensic anthropologists are also helpful in identifying victims of a mass disaster such as a plane crash. When such a tragedy occurs, forensic anthropologists can help identify victims us- ing the collection of bone fragments. Usually, the identification of the remains will depend on medical records, especially dental records of the individuals. However, definite identification of remains can be made only by analyzing the decedent’s DNA profile, fingerprints, or medical records. Recovered remains may still contain some soft tissue material, such as the tissue of the hand, which may yield a DNA profile for identification purposes. If the tissue is dried out, it may be possible to rehydrate it to recover fingerprints also.

Role of the Forensic Entomologist The study of insects and their relation to a criminal investigation is known as forensic entomology. In practice, forensic entomology is commonly used to estimate the time of death when the circumstances surrounding the crime are unknown. This determination can be carried out by observing the stage of development of maggots or insects’ sequence of arrival.

Determining Time of Death After decomposition begins, necrophilious insects, or insects that feed on dead tissue, are the first to infest the body, usually within 24 hours. The most common and important of these is the blowfly, recognized by its green or blue color. Blowfly eggs are laid in human remains and ultimately hatch into maggots, or fly larvae, that consume human organs and tissues (see Figure 5–20). Typically, a single blowfly can lay up to 2,000 eggs during its lifetime. The resulting larvae gather and feed as a “maggot mass” on the decomposing remains. Forensic entomologists can approximate how long a body has been left exposed by examining the stage of development of the fly larvae. This kind of determination is best for a timeline of hours to approximately one month because the blowfly goes through the stages of its life cycle at a known sequence and in known time intervals that span this period. By determining the most developed stage of fly found on the body, entomologists can approximate the postmortem interval (PMI), or the time that has elapsed since death (see Figure 5–21). Newly emerged flies are of important forensic interest, as they indicate that an entire blowfly cycle has been completed on the decomposing body. Likewise, empty pupal cases indicate that a fly has completed its entire life cycle on the body. Flies known as cheese skippers are primarily found on human corpses in the later stages of decomposition, long after the blowflies have left the corpse.

Time determinations based on the blowfly cycle are not always straight- forward, however. The time required for each stage of development is af- fected by environmental influences such as geographical location, climate, weather conditions, and the presence of drugs. For example, cold tempera- tures hinder the development of fly eggs into adult flies. The forensic ento- mologist must consider these conditions when estimating the PMI.

Information about the arrival of other species of insects may also help determine the PMI. The sequence of arrival of these groups depends mostly on the body’s natural decomposition process. Predator insects generally arrive and prey on the necrophilious insects. Several kinds of beetles will be found, either feeding directly on the corpse’s tissues or as predators feeding on blowfly eggs and maggots present on the corpse. Next, omnivore insects arrive at the body. These insects feed on the body, on other insects, and on any surrounding vegetation. Ants and wasps are an example of omnivore insects. Last comes the arrival of indigenous in- sects, such as spiders, whose presence on or near the body is coincidental as they move about their environment.

forensic entomology The study of insect matter, growth patterns, and succession of arrival at a crime scene to determine the time since death.

FIGURE 5–20 A scanning electron micrograph of two-hour-old blowfly maggots.

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postmortem interval (PMI) The length of time that has elapsed since a person has died. If the time is not known, a number of medi- cal or scientific techniques may be used to estimate it.

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The Danielle Van Dam Murder Case Sometime during the night of February 1, 2002, 7-year-old

Springs suburb of San Diego, California. On February 27, three and a half weeks later, searchers found her naked body in a trash-covered lot about 25 miles from her home. Because of the high degree of decomposition of the girl’s remains, the medical examiner could not pinpoint the exact time of the girl’s death. Her neighbor, 50-year-old engineer David West- erfield, was accused of kidnapping Danielle, killing her, and dumping her body in the desert. During the subsequent inves- tigation, Danielle’s blood was found on Westerfield’s clothes,

pornography was found on his home computer. The actual time of the 7-year-old’s death became a central

issue during the murder trial. Westerfield had been under con- stant police surveillance since February 4. Any suggestion that

Danielle was placed at the dump site after that date would have eliminated him as a suspect. Conflicting expert testimony was elicited from forensic entomologists who were called on to es- timate when the body was dumped. The forensic entomologist who went to the dump site, witnessed the autopsy, and collected and analyzed insects from both locations estimated that Dani- elle died between February 16 and 18. A forensic entomologist and a forensic anthropologist both called to testify on behalf of the prosecution noted that the very hot, very dry weather at the dump site might have mummified Danielle’s body almost im- mediately, thus causing a delay in the flies colonizing the body.

The jurors convicted Westerfield of the kidnapping and

and settled a wrongful death suit against Westerfield requir- ing his automotive and homeowner’s insurance carriers to pay

$400,000 and $1 million.

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Larva Stage III

Postfeeding

Puparium

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FIGURE 5–21 Typical blowfly life cycle from egg deposition to adult fly emergence. This cycle is representative of any one of nearly ninety species of blowflies in North America.

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Other Contributions of Forensic Entomology Entomological evidence can also provide other pertinent information. In general, insects first colonize the body’s naturally moist orifices. However, if open wounds are present, they will colo- nize there first. Although the decomposition processes may conceal wounds, colonization away from natural orifices may indicate the locations of wounds on the body. If maggots are found ex- tensively on the hands and forearms, for example, this suggests the presence of defensive wounds on the victim. Insects that have fed on the body may also have accumulated any drugs present in the flesh, and analyzing these insects can yield the identity of these drugs.

If resources allow, all insect evidence should be carefully collected by a forensic entomol- ogy expert. When this is not possible, collection should be carried out by an investigator with experience in death investigation. The entire body and the area where insect evidence was found must be photographed and documented before collection. Insect specimens should be taken from each area on the body where they are found and labeled to show where they were collected from.

chapter summary Forensic pathologists associated with the medical examin- er’s or coroner’s office are responsible for determining the cause of a an undetermined or unexpected death. Although both the coroner’s office and the medical examiner’s of- fice are charged with investigating suspicious deaths, only the pathologist is trained to perform an autopsy. The tasks of examining the body for cause and manner of death and recording the results in the death certificate are all respon- sibilities of both offices. Protection of the body and the overall scene is of paramount importance, as is the ultimate removal of the body in a medically acceptable manner. A primary objective of the autopsy is to determine the cause of death. The cause of death is defined as that which initi- ates the series of events ending in death. The most impor- tant determination in a violent death is the character of the injury that started the chain of events that resulted in death. Some of the more common causes of death are: blunt-force injury, sharp-force injury, asphyxia, gunshot wounds, and substance abuse.

An autopsy, in its broadest definition, is simply the ex- amination of a body after death. The forensic autopsy consists of an external examination and an internal examination of the condition of the body and the clothing. The dissection of the human body generally entails the removal of all internal or- gans through a Y-shaped incision beginning at the top of each shoulder and extending down to the pubic bone. The internal

examination entails weighing, dissecting, and sectioning each organ of the body. Blood is often tested to determine the pres- ence and levels of alcohol and drugs. The manner in which death occurred is classified in death certifications as one of five categories: homicide, suicide, accidental, natural, or undetermined.

After death the body undergoes a process known as al- gor mortis in which it will continually adjust to equalize with the environmental temperature. Another condition beginning when circulation ceases is livor mortis. When the human heart stops pumping, the blood begins to settle in the parts of the body closest to the ground. The skin appears bluish-purple in these areas. Immediately following death, a chemical change known as rigor mortis occurs in the muscles, causing them to become rigid.

Forensic anthropology is concerned primarily with the identification and examination of human skeletal remains. The gender of the decedent can be determined by the size and shape of various skeletal features, especially those in the pelvis and skull, or cranium. The height of the victim when alive can be estimated by measuring the long bones of the skeleton, especially those in the lower limbs. Forensic en- tomologists can approximate how long a body has been left exposed by examining the stage of development of the fly larvae on the body.

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120 CHAPTER 5

1. The titles of ___________ and ___________ are often used interchangeably, but there are significant differ- ences in their job descriptions.

2. True or False: The medical examiner is an elected official and is not required to possess a medical degree. ___________

3. Although both a coroner and a forensic pathologist are charged with investigating a suspicious death, only the ___________ is trained to perform an autopsy.

4. True or False: If it appears that a victim did not shoot himself or herself or anyone else, the victim’s hands should not be swabbed. ___________

5. The primary objective of the autopsy is to determine the ___________.

6. True or False: The manner of death is defined as that which initiates the series of events ending in death. ___________

7. A(n) ___________-force injury can abrade and crush tissue.

8. True or False: The outward appearance of the injuries will always match the injuries sustained inside the body. ___________

9. Wounds on a victim’s forearm may be ___________ wounds.

10. True or False: A lack of any defense wounds can lead a pathologist to believe that the victim was either un- conscious or somehow tied up during the assault. ___________

11. Asphyxia encompasses a variety of conditions that in- volve interference with the intake of ___________.

12. True or False: Death at a fire scene is primarily caused by the extremely toxic gas carbon monoxide. ___________

13. The protein in red blood cells that transports oxygen is known as ___________.

14. True or False: High levels of carbon monoxide must be present for a victim to become disoriented and lose con- sciousness. ___________

15. True or False: Carbon monoxide will continue to build up in the body after death. ___________

16. Carbon monoxide levels and the presence of soot can be used to determine whether the individual was ___________ at the time of the fire.

17. on the eyelids, cheeks, and forehead.

18. Petechiae are caused by the escaping of blood into the tissue as a result of ___________ bursting.

19. True or False: Petechiae are more common in hangings than strangulation deaths. ___________

20. True or False: Typically the hyoid bone and thyroid car- tilage are not fractured in hanging cases. ___________

21. True or False: For gunshot victims, the cause of death can be listed as a gunshot wound. ___________

22. True or False: Because drug abuse is so common, the forensic pathologist will routinely test for the presence of drugs in nearly all investigations. ___________

23. A(n) ___________ in its broadest definition is simply the examination of a body after death.

24. True or False: There are two types of autopsies: a forensic/medicolegal autopsy and a clinical/hospital autopsy. ___________

25. The autopsy consists of a(n) ___________ examination and a(n) ___________ examination.

26. The discharge from a firearm will produce characteristic markings on the skin known as ___________.

27. True or False: X-ray examinations are most commonly performed in gunshot wound cases and stab wound cases. ___________

28. Pulmonary ___________, or fluid accumulation in the lungs, is frequently found in victims of chronic cocaine and amphetamine abuse.

29. True or False: The liver can contain partially digested or dissolved pills. ___________

30. True or False: The ideal location to take a blood sample is from the heart. ___________

31. ___________ is the redistribution of drugs after death.

32. True or False: General testing for poisons is not a routine procedure carried out by the pathologist. ______________

33. A body that displays a cherry-red discoloration of- ten leads a pathologist to suspect poisoning by ______________.

34. True or False: A pathologist can often give an exact time of death. ___________

review questions

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application and critical thinking

1. Rigor mortis, livor mortis, and algor mortis are all used to help determine time of death. However, each method has its limitations. For each method, describe at least one condition that would render that method unsuitable or inaccurate for determining time of death.

2. What kind of forensic expert would most likely be asked to help identify human remains in each of the following conditions?

a. A body that has been decomposing for a day or two

b. Fragmentary remains of a few arm bones and part of a jaw

c. A skeleton that is missing its skull

3. Identify a reasonable manner of death for each of the following situations:

a. A contact wound to the back of the head

b. An elevated carboxyhemoglobin blood level in a fire victim

c. A fractured hyoid bone

d. Death by overdose of a first-time user of alcohol

e. A gunshot wound to the chest from a distance of 3 feet

f. Sudden death of a young chronic user of cocaine

4. In cooperation with the medical examiner or coroner, evidence retrieved from a deceased victim and sent to the crime lab should include which items?

35. The process of the body’s continually decreasing in tem- perature after death until it reaches the environmental temperature is known as ___________.

36. The process of the blood settling in parts of the body closest to the ground after death is known as ___________.

37. True or False: Different lividity patterns on a body may indicate that the body was moved after death but before livor mortis had fully fixed. ___________

38. Levels of ___________ in the ocular fluid can help indi- cate the time of death.

39. After death, two decomposition processes take place: ___________ and ___________.

40. The female bone structure differs from the male struc- ture within the ___________ area because of a woman’s child-bearing capabilities.

41. True or False: A definite identification of remains cannot be made through the analysis of the dece- dent’s DNA profile, fingerprints, or medical records. ___________

42. True or False: A site where human remains are found must be treated as a crime scene, and the site and sur- rounding area should be secured, searched, and carefully processed. ___________

43. The field of ___________ takes advantage of the du- rable nature of bones over a long period of time to ex- amine and identify human skeletal remains through a multitude of individual characteristics.

44. The study of insects and their relation to a criminal in- vestigation, known as ___________, is commonly used to estimate the time of death when the circumstances surrounding the crime are unknown.

45. By determining the oldest stage of fly found on the body and taking environmental factors into consider- ation, entomologists can approximate the ___________ interval.

46. True or False: Another method to determine PMI is by observing the schedule of arrival of different insects spe- cies on the body. ___________

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122 CHAPTER 5

Cranium

Size Medium Forehead Rounded, projected outward Mastoid process Absent Jaw Angle 5 110 degrees Teeth All permanent Sagittal suture Not fused Coronal suture Not fused Eye orbits Squared Nasal cavity Large, wide Incisors Smooth

Pelvis

Opening See figure Sacrum See figure Subpubic angle 90–100 degrees

Long Bones

Femur Fully fused, 44.1 cm long Clavicle Fully fused Gender _____ Ancestry _____ Age Range _____ Height _____

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5. Creating a Forensic Anthropology Victim Profile A nearly complete human skeleton has been found. The skeleton has the features shown in the accompanying

table and image. Approximate the gender, ancestry, age range, and height of the individual based on this information.

6. Sequence of Insect Arrival in Forensic Entomology The following images depict the sequence of events at

the site of a decomposing body. Place the arrival events in order of occurrence from earliest to latest.

(a) (b)

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further references

Spitz, W. U., and D. J. Spitz, eds., Spitz and Fisher’s Medicolegal Investigation of Death: Guidelines for the Application of Pathology to Crime Investigation, 4th ed. Springfield, Ill.: Charles C. Thomas, 2006.

DiMaio, V. J. M., and S. E. Dana, Handbook of Forensic Pathology, 2nd ed. Boca Raton, Fla.: CRC Press, 2006.

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James Earl Ray: Conspirator or Lone Gunman?

Since his arrest in 1968 for the assassination of Dr. Martin Luther King, Jr., endless speculation has swirled around the motives and connections of James Earl Ray. Ray was a career criminal who was serving time for armed robbery when he escaped from the Missouri State Prison almost one year before the assassination. On April 3, 1968, Ray arrived in Memphis, Tennessee. The next day he rented a room at Bessie Brewer’s Rooming House, across the street from the Lorraine Motel where Dr. King was staying.

At 6:00 p.m., Dr. King left his second-story motel room and stepped onto the balcony of the Lorraine Motel. As King turned toward his room, a shot rang out, striking the civil rights activist. Nothing could be done to revive him, and Dr. King was pronounced dead at 7:05 p.m. As the assailant ran on foot from Bessie Brewer’s, he left a blanket-covered package in front of a nearby building and then drove off in a white Mustang. The package was later shown to contain a high-powered rifle

equipped with a scope, a radio, some clothes, a pair of binoculars, a couple of beer cans, and a receipt for

the binoculars. Almost a week after the shooting, the white Mustang was found abandoned in Atlanta, Georgia.

Fingerprints later identified as James Earl Ray’s were found in the Mustang, on the rifle, on the binoculars, and on a beer can. In 1969, Ray entered a guilty plea in return for a sentence of 99 years. Although a variety of conspiracy theories surround this crime, the indisputable fact is that a fingerprint put the rifle that killed Martin Luther King, Jr., in the hands of James Earl Ray.

headline news ©

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fingerprints

anthropometry arch digital imaging fluoresce iodine fuming latent fingerprint livescan loop ninhydrin Physical Developer pixel plastic print portrait parlé ridge characteristics

(minutiae) sublimation superglue fuming visible print whorl

KEY TERMS

chapter 6

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Know the common ridge characteristics of a fingerprint

List the three major fingerprint patterns and their respective subclasses

Distinguish visible, plastic, and latent fingerprints

Describe the concept of an automated fingerprint identification system (AFIS)

List the techniques for developing latent fingerprints on porous and nonporous objects

Describe the proper procedures for preserving a developed latent fingerprint

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126 CHAPTER 6

History of Fingerprinting Since the beginnings of criminal investigation, police have sought an infallible means of human identification. The first systematic attempt at personal identification was devised and introduced by a French police expert, Alphonse Bertillon, in 1883. The Bertillon system relied on a detailed description (portrait parlé) of the subject, combined with full-length and profile photographs and a system of precise body measurements known as anthropometry.

The use of anthropometry as a method of identification rested on the premise that the dimen- sions of the human bone system remained fixed from age 20 until death. Skeleton sizes were thought to be so extremely diverse that no two individuals could have exactly the same measure- ments. Bertillon recommended routine taking of eleven measurements of the human anatomy. These included height, reach, width of head, and length of the left foot (see Figure 1–3).

For two decades, this system was considered the most accurate method of identification. But in the first years of the new century, police began to appreciate and accept a system of iden- tification based on the classification of finger ridge patterns known as fingerprints. Today, the fingerprint is the pillar of modern criminal identification.

Early Use of Fingerprints Evidence exists that the Chinese used the fingerprint to sign legal documents as far back as three thousand years ago. However, whether this practice was performed for ceremonial custom or as a means of personal identity remains a point of conjecture lost to history. In any case, the examples of fingerprinting in ancient history are ambiguous, and the few that exist did not contribute to the development of fingerprinting techniques as we know them today.

Several years before Bertillon began work on his system, William Herschel, an Eng- lish civil servant stationed in India, started the practice of requiring Indian citizens to sign contracts with the imprint of their right hand, which was pressed against a stamp pad for the purpose. The motives for Herschel’s requirement remain unclear; he may have envisioned fingerprinting as a means of personal identification or just as a form of the Hindu custom that a trace of bodily contact was more binding than a signature on a contract. In any case, he did not publish anything about his activities until after a Scottish physician, Henry Fauld, work- ing in a hospital in Japan, published his views on the potential application of fingerprinting to personal identification.

In 1880, Fauld suggested that skin ridge patterns could be important for the identification of criminals. He told about a thief who left his fingerprint on a whitewashed wall, and how in comparing these prints with those of a suspect, he found that they were quite different. A few days later another suspect was found whose fingerprints compared with those on the wall. When confronted with this evidence, the individual confessed to the crime.

Fauld was convinced that fingerprints furnished infallible proof of identification. He even offered to set up, at his own expense, a fingerprint bureau at Scotland Yard to test the practical- ity of the method. But his offer was rejected in favor of the Bertillon system. This decision was reversed less than two decades later.

Early Classification of Fingerprints The extensive research into fingerprinting conducted by another Englishman, Francis Galton, provided the needed impetus that made police agencies aware of its potential application. In 1892, Galton published his classic textbook Finger Prints, the first book of its kind on the sub- ject. In his book, he discussed the anatomy of fingerprints and suggested methods for recording them. Galton also proposed assigning fingerprints to three pattern types—loops, arches, and whorls. Most important, the book demonstrated that no two prints were identical and that an individual’s prints remained unchanged from year to year. At Galton’s insistence, the British government adopted fingerprinting as a supplement to the Bertillon system.

The next step in the development of fingerprint technology was the creation of classifica- tion systems capable of filing thousands of prints in a logical and searchable sequence. Dr. Juan Vucetich, an Argentinian police officer fascinated by Galton’s work, devised a workable concept in 1891. His classification system has been refined over the years and is still widely used today in most Spanish-speaking countries. In 1897, another classification system was proposed by an Englishman, Sir Edward Richard Henry. Four years later, Henry’s system was adopted by

portrait parlé A verbal description of a perpetra- tor’s physical characteristics and dress provided by an eyewitness.

anthropometry A system of identification of indi- viduals by measurement of parts of the body, developed by Alphonse Bertillon.

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Scotland Yard. Today, most English-speaking countries, including the United States, use some version of Henry’s classification system to file fingerprints.

Adoption of Fingerprinting Early in the 20th century, Bertillon’s measurement system began to fall into disfavor. Its results were highly susceptible to error, particularly when the measurements were taken by people who were not thoroughly trained. The method was dealt its most severe and notable setback in 1903 when a convict, Will West, arrived at Fort Leavenworth prison. A routine check of the prison files startlingly revealed that a William West, already in the prison, could not be distinguished from the new prisoner by body measurements or even by photographs. In fact, the two men looked just like twins, and their measurements were practically the same. Subsequently, fingerprints of the prisoners clearly distinguished them.

In the United States, the first systematic and official use of fingerprints for personal iden- tification was adopted by the New York City Civil Service Commission in 1901. The method was used for certifying all civil service applications. Several American police officials received instruction in fingerprint identification at the 1904 World’s Fair in St. Louis from representatives of Scotland Yard. After the fair and the Will West incident, fingerprinting began to be used in earnest in all major cities of the United States. In 1924, the fingerprint records of the Bureau of Investigation and Leavenworth were merged to form the nucleus of the identification records of the new Federal Bureau of Investigation. The FBI has the largest collection of fingerprints in the world. By the beginning of World War I, England and practically all of Europe had adopted fingerprinting as their primary method of identifying criminals.

In 1999, the admissibility of fingerprint evidence was challenged in the case of United States v. Byron C. Mitchell in the Eastern District of Pennsylvania. The defendant’s attorneys argued that fingerprints could not be proven unique under the guidelines cited in Daubert (see pages 16–18). Government experts vigorously disputed this claim. After a four-and-a-half-day Daubert hearing, the judge upheld the admissibility of fingerprints as scientific evidence and ruled that (1) human friction ridges are unique and permanent and (2) human friction ridge skin arrangements are unique and permanent.

Fundamental Principles of Fingerprints First Principle: A Fingerprint Is an Individual Characteristic; No Two Fingers Have Yet Been Found to Possess Identical Ridge Characteristics The acceptance of fingerprint evidence by the courts has always been predicated on the as- sumption that no two individuals have identical fingerprints. Early fingerprint experts consis- tently referred to Galton’s calculation, showing the possible existence of 64 billion different fingerprints, to support this contention. Later, researchers questioned the validity of Galton’s figures and attempted to devise mathematical models to better approximate this value. How- ever, no matter what mathematical model one refers to, the conclusions are always the same: the probability for the existence of two identical fingerprint patterns in the world’s population is extremely small.

Not only is this principle supported by theoretical calculations, but just as important, it is verified by the millions of individuals who have had their prints classified during the past 120 years—no two have ever been found to be identical. The FBI has nearly 75 million finger- print records in its computer database and has yet to find an identical image belonging to two different people.

RIDGE CHARACTERISTICS The individuality of a fingerprint is not determined by its general shape or pattern but by a careful study of its ridge characteristics (also known as minutiae). The identity, number, and relative location of characteristics such as those illustrated in Figure 6–1 impart individuality to a fingerprint. If two prints are to match, they must reveal characteristics that not only are identical but have the same relative location to one another in a print. In a judicial proceeding, a point-by-point comparison must be demonstrated by the expert, using charts similar to the one shown in Figure 6–2, in order to prove the identity of an individual.

ridge characteristics (minutiae) Ridge endings, bifurcations, enclosures, and other ridge details, which must match in two fingerprints in order for their common origin to be established.

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If an expert were asked to compare the characteristics of the complete fingerprint, no dif- ficulty would be encountered in completing such an assignment; the average fingerprint has as many as 150 individual ridge characteristics. However, most prints recovered at crime scenes are partial impressions, showing only a segment of the entire print. Under these circumstances, the expert can compare only a small number of ridge characteristics from the recovered print to a known recorded print.

RIDGE COMPARISONS For years, experts have debated how many ridge comparisons are necessary to identify two fingerprints as the same. Numbers that range from 8 to 16 have been suggested as being sufficient to meet the criteria of individuality. However, the difficulty in establishing such a minimum is that no comprehensive statistical study has ever been undertaken to determine the frequency of occurrence of different ridge characteristics and their relative

Ridge

Endings

Bifurcation Ridge Ending

Enclosure

Ridge Island (Ridge Dot)

Bifurcation

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locations. Until such a study is undertaken and completed, no meaningful guidelines can be established for defining the uniqueness of a fingerprint.

In 1973, the International Association for Identification, after a three-year study of this ques- tion, concluded that “no valid basis exists for requiring a predetermined minimum number of fric- tion ridge characteristics which must be present in two impressions in order to establish positive identification.” Hence, the final determination must be based on the experience and knowledge of the expert, with the understanding that others may profess honest differences of opinion on the uniqueness of a fingerprint if the question of minimal number of ridge characteristics exists. In 1995, members of the international fingerprint community at a conference in Israel issued the Ne’urim Declaration, which supported the 1973 International Association for Identification resolution.

Second Principle: A Fingerprint Remains Unchanged During an Individual’s Lifetime Fingerprints are a reproduction of friction skin ridges found on the palm side of the fingers and thumbs. Similar friction skin can also be found on the surface of the palms and soles of the feet. Apparently, these skin surfaces have been designed by nature to provide our bodies with a firmer grasp and a resistance to slippage. A visual inspection of friction skin reveals a series of lines corresponding to hills (ridges) and valleys (grooves). The shape and form of the skin ridges are what one sees as the black lines of an inked fingerprint impression.

STRUCTURE OF THE SKIN Skin is composed of layers of cells. Those nearest the surface make up the outer portion of the skin known as the epidermis, and the inner skin is known as the dermis. A cross section of skin (see Figure 6–3) reveals a boundary of cells separating the epidermis and dermis. The shape of this boundary, made up of dermal papillae, determines the form and pattern of the ridges on the surface of the skin. Once the dermal papillae develop in the human fetus, the ridge patterns remain unchanged throughout life except to enlarge during growth.

Each skin ridge is populated by a single row of pores that are the openings for ducts lead- ing from the sweat glands. Through these pores, perspiration is discharged and deposited on the surface of the skin. Once the finger touches a surface, perspiration, along with oils that may have been picked up by touching the hairy portions of the body, is transferred onto that surface, thereby leaving an impression of the finger’s ridge pattern (a fingerprint). Prints deposited in this manner are invisible to the eye and are commonly referred to as latent fingerprints.

Ridge island

Sweat pores

Epidermis

Papillae

Dermis

Duct of sweat gland

Sweat gland

Nerves of touch

FIGURE 6–3 Cross-section of human skin.

latent fingerprint A fingerprint made by the deposit of oils and/or perspiration; it is in- visible to the naked eye.

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130 CHAPTER 6

CHANGING FINGERPRINTS Although it is impossible to change one’s fingerprints, there has been no lack of effort on the part of some criminals to obscure them. If an injury reaches deeply enough into the skin and damages the dermal papillae, a permanent scar will form. However, for this to happen, such a wound would have to penetrate 1 to 2 millimeters beneath the skin’s surface. Indeed, efforts at intentionally scarring the skin can only be self-defeating, for it would be totally impossible to obliterate all of the ridge characteristics on the hand, and the presence of permanent scars merely provides new characteristics for identification.

Perhaps the most publicized attempt at obliteration was that of the notorious gangster John Dillinger, who tried to destroy his own fingerprints by applying a corrosive acid to them. Prints taken at the morgue after he was shot to death, compared with fingerprints recorded at the time of a previous arrest, proved that his efforts had been fruitless (see Figure 6–4).

Third Principle: Fingerprints Have General Ridge Patterns That Permit Them to Be Systematically Classified All fingerprints are divided into three classes on the basis of their general pattern: loops, whorls, and arches. Sixty to 65 percent of the population have loops, 30 to 35 percent have whorls, and about 5 percent have arches. These three classes form the basis for all ten-finger classification systems presently in use.

LOOPS A typical loop pattern is illustrated in Figure 6–5. A loop must have one or more ridges entering from one side of the print, recurving, and exiting from the same side. If the loop opens toward the little finger, it is called an ulnar loop; if it opens toward the thumb, it is a radial loop. The pattern area of the loop is surrounded by two diverging ridges known as type lines. The ridge point at or nearest the type-line divergence and located at or directly in front of the point of divergence is known as the delta. To many, a fingerprint delta resembles the silt formation that builds up as a river flows into the entrance of a lake—hence, the analogy to the geological formation known as a delta. All loops must have one delta. The core, as the name suggests, is the approximate center of the pattern.

WHORLS Whorls are actually divided into four distinct groups, as shown in Figure 6–6: plain, central pocket loop, double loop, and accidental. All whorl patterns must have type lines and at least two deltas. A plain whorl and a central pocket loop have at least one ridge that makes a complete circuit. This ridge may be in the form of a spiral, an oval, or any variant of a circle. If an imaginary line drawn between the two deltas contained within these two patterns touches any one of the spiral ridges, the pattern is a plain whorl. If no such ridge is touched, the pattern is a central pocket loop.

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loop A class of fingerprints character- ized by ridge lines that enter from one side of the pattern and curve around to exit from the same side of the pattern.

whorl A class of fingerprints that includes ridge patterns that are generally rounded or circular in shape and have two deltas.

arch A class of fingerprints characterized by ridge lines that enter the print from one side and flow out the other side.

FIGURE 6–4 The right index finger impression of John Dillinger, before scarification on the left and afterward on the right. Comparison is proved by the 14 matching ridge characteristics.

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As the name implies, the double loop is made up of two loops combined into one fingerprint. Any whorl classified as an accidental either contains two or more patterns (not including the plain arch) or is a pattern not covered by other categories. Hence, an accidental may consist of a combination loop and plain whorl or loop and tented arch.

ARCHES Arches, the least common of the three general patterns, are subdivided into two distinct groups: plain arches and tented arches, as shown in Figure 6–7. The plain arch is the simplest of all fingerprint patterns; it is formed by ridges entering from one side of the print and exiting on the opposite side. Generally, these ridges tend to rise in the center of the pattern, forming a wavelike pattern. The tented arch is similar to the plain arch except that instead of rising smoothly at the center, there is a sharp upthrust or spike, or the ridges meet at an angle that is less than 90 degrees.1 Arches do not have type lines, deltas, or cores.

With a knowledge of basic fingerprint pattern classes, we can now begin to develop an ap- preciation for fingerprint classification systems. However, the subject is far more complex than

1 A tented arch is also any pattern that resembles a loop but lacks one of the essential requirements for classification as a loop.

Type line

Delta

Type line

Core

FIGURE 6–5 Loop pattern.

Plain whorl Central pocket loop

Double loop Accidental

FIGURE 6–6 Whorl patterns.

Plain Tented

FIGURE 6–7 Arch patterns.

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can be described in a textbook of this nature. The student seeking a more detailed treatment of the subject would do well to consult the references cited at the end of the chapter.

Classification of Fingerprints The original Henry system, as it was adopted by Scotland Yard in 1901, converted ridge patterns on all ten fingers into a series of letters and numbers arranged in the form of a fraction. However, the system as it was originally designed could accommodate files of up to only 100,000 sets of prints; thus, as collections grew in size, it became necessary to expand the capacity of the clas- sification system. In the United States, the FBI, faced with the problem of filing ever-increasing numbers of prints, expanded its classification capacity by modifying and extending the original Henry system. These modifications are collectively known as the FBI system and are used by most agencies in the United States today.

The Primary Classification Although we will not discuss all of the different divisions of the FBI system, a description of just one part, the primary classification, will provide an interesting insight into the process of fingerprint classification.

The primary classification is part of the original Henry system and provides the first clas- sification step in the FBI system. Using this classification alone, all of the fingerprint cards in the world could be divided into 1,024 groups. The first step in obtaining the primary classification is to pair up fingers, placing one finger in the numerator of a fraction, the other in the denominator. The fingers are paired in the following sequence:

R. Index R. Ring L. Thumb L. Middle L. Little

R. Thumb R. Middle R. Little L. Index L. Ring

The presence or absence of the whorl pattern is the basis for determination of the primary classification. If a whorl pattern is found on any finger of the first pair, it is assigned a value of 16; on the second pair, a value of 8; on the third pair, a value of 4; on the fourth pair, a value

location of ridge pores, breaks, creases, scars, and other permanent minutiae. During the comparison phase, the examiner compares the latent print side by side with an exemplar print in its totality.

The evaluation stage requires one of three de- cisions to be arrived at. The decisions that can be reported are: identification (the latent print and ex- emplar came from the same source); exclusion (the la- tent print and exemplar did not come from the same source); inconclusive (one cannot determine that the latent print and exemplar came from the same source, or not, to a sufficiently strong level of certainty).

The final step in the process involves verification of the examiner’s result. It requires an independent examination of the questioned and known prints by a second examiner. Ultimately, a consensus between the two examiners must be arrived at before a final conclusion is drawn.

The ACE-V Process

ACE-V is an acronym for the four-step process— analysis, comparison, evaluation, and verification— used to identify and individualize a fingerprint. The first step requires the examiner to identify any distor- tions associated with the friction ridges, as well as any external factors, such as surface or deposition factors or processing techniques, that may impinge on the print’s appearance. If the examiner determines the latent print adequate, he or she will declare the print to be of value for the comparison stage.

The comparison step requires the examiner to com- pare the questioned print to the known print at three lev- els. Level 1 looks at the general ridge flow and pattern configuration. Level 2 includes locating and comparing ridge characteristics, or minutiae. Level 2 details can in- dividualize a print. Level 3 includes the examination and

Inside the Science

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of 2; and on the last pair, a value of 1. Any finger with an arch or loop pattern is assigned a value of 0.

After values for all ten fingers are obtained in this manner, they are totaled, and 1 is added to both the numerator and denominator. The fraction thus obtained is the primary classification. For example, if the right index and right middle fingers are whorls and all the others are loops, the primary classification is

16 1 0 1 0 1 0 1 0 1 1 =

0 1 8 1 0 1 0 1 0 1 1 9

Approximately 25 percent of the population falls into the 1/1 category; that is, all their fin- gers have either loops or arches.

A fingerprint classification system cannot in itself unequivocally identify an individual; it merely provides the fingerprint examiner with a number of candidates, all of whom have an indistinguishable set of prints in the system’s file. The identification must always be made by a final visual comparison of the suspect print’s and file print’s ridge characteristics; only these features can impart individuality to a fingerprint. Although ridge patterns impart class charac- teristics to the print, the type and position of ridge characteristics give it its individual character.

Automated Fingerprint Identification Systems The Henry system and its subclassifications have proven to be a cumbersome system for storing, retrieving, and searching for fingerprints, particularly as fingerprint collections grow in size. Nevertheless, until the emergence of fingerprint computer technology, this manual approach was the only viable method for the maintenance of fingerprint col- lections. Since 1970, technological advances have made possible the classification and retrieval of fingerprints by computers. Automated Fingerprint Identification Systems (AFISs) have proliferated throughout the law enforcement community.

In 1999, the FBI initiated full operation of the Integrated Automated Fingerprint Identification System (IAFIS), the largest AFIS in the United States, which links state AFIS computers with the FBI database. This database contains nearly 50 million finger- print records. However, an AFIS can come in all sizes ranging from the FBI’s to inde- pendent systems operated by cities, counties, and other agencies of local government (see Figure 6–8). Unfortunately, these local systems often are not linked to the state’s AFIS system because of differences in software configurations.

How AFIS Works The heart of AFIS technology is the ability of a computer to scan and digitally encode fingerprints so that they can be subject to high-speed computer processing. The AFIS uses automatic scanning devices that convert the image of a fingerprint into digital minutiae that contain data showing ridges at their points of termination (ridge end- ings) and the branching of ridges into two ridges (bifurcations). The relative position and orientation of the minutiae are also determined, allowing the computer to store each fingerprint in the form of a digitally recorded geometric pattern.

The computer’s search algorithm determines the degree of correlation between the location and relationship of the minutiae for both the search and file prints. In this manner, a computer can make thousands of fingerprint comparisons in a second; for example, a set of ten fingerprints can be searched against a file of 500,000 ten-finger prints (ten-prints) in about eight-tenths of a second. During the search for a match, the computer uses a scoring system that assigns prints to each of the criteria set by an operator. When the search is complete, the com- puter produces a list of file prints that have the closest correlation to the search prints. All of the selected prints are then examined by a trained fingerprint expert, who makes the final verification of the print’s identity. Thus, the AFIS makes no final decisions on the identity of a fingerprint, leaving this function to the eyes of a trained examiner.

FIGURE 6–8 An AFIS system designed for use by local law enforcement agencies.

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The speed and accuracy of ten-print processing by AFIS have made possible the search of single latent crime-scene fingerprints against an entire file’s print collection. Before the AFIS, police were usually restricted to comparing crime-scene fingerprints against those of known suspects. The impact of the AFIS on no-suspect cases has been dramatic. Minutes after California’s AFIS network received its first assignment, the computer scored a direct hit by identifying an individual who had committed 15 murders, terrorizing the city of Los Angeles. Police estimate that it would have taken a single technician, manually searching the city’s 1.7 million print cards, 67 years to come up with the perpetrator’s prints. With the AFIS, the search took approximately 20 minutes. In its first year of operation, San Francisco’s AFIS computer conducted 5,514 latent fingerprint searches and achieved 1,001 identifications—a hit rate of 18 percent. This compares to the previous year’s average of 8 percent for manual latent-print searches.

As an example of how an AFIS computer operates, one system has been designed to au- tomatically filter out imperfections in a latent print, enhance its image, and create a graphic representation of the fingerprint’s ridge endings and bifurcations and their direction. The print is then computer searched against file prints. The image of the latent print and a matching file print are then displayed side by side on a high-resolution video monitor, as shown in Figure 6–9. The matching latent and file prints are then verified and charted by a fingerprint examiner at a video workstation.

The stereotypical image of a booking officer rolling inked fingers onto a standard ten-print card for ultimate transmission to a database has, for the most part, been replaced with digital- capture devices (livescan) that eliminate ink and paper. The livescan captures the image on each finger and the palms as they are lightly pressed against a glass platen. These livescan images can then be sent to the AFIS database electronically, so that within minutes the booking agency can enter the fingerprint record into the AFIS database and search the database for previous entries of the same individual (see Figure 6–10).

FIGURE 6–9 A side-by-side comparison of a latent print against a file fingerprint is conducted in seconds, and their similarity rating (SIM) is displayed on the upper-left portion of the screen.

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FIGURE 6–10 Livescan technology en- ables law enforcement to print and compare a subject’s fingerprints rap- idly, without inking the fingerprints.

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livescan An inkless device that captures the digital images of fingerprints and palm prints and electronically transmits the images to an AFIS.

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Considerations with AFIS AFIS has fundamentally changed the way criminal investigators operate, allowing them to spend less time developing suspect lists and more time investigating the suspects generated by the com- puter. However, investigators must be cautioned against overreliance on a computer. Sometimes a latent print does not make a hit because of the poor quality of the file print. To avoid these po- tential problems, investigators must still print all known suspects in a case and manually search these prints against the crime-scene prints.

AFIS computers are available from several different suppliers. Each system scans finger- print images and detects and records information about minutiae (ridge endings and bifurca- tions); however, they do not all incorporate exactly the same features, coordinate systems, or units of measure to record fingerprint information. These software incompatibilities often mean that, although state systems can communicate with the FBI’s IAFIS, they may not com- municate with each other directly. Likewise, local and state systems frequently cannot share information with each other. Many of these technical problems will be resolved as more agen- cies follow transmission standards developed by the National Institute of Standards and Tech- nology and the FBI.

Methods of Detecting Fingerprints Through common usage, the term latent fingerprint has come to be associated with any finger- print discovered at a crime scene. Sometimes, however, prints found at the scene of a crime are quite visible to the eye, and the word latent is a misnomer. Actually, there are three kinds of

The Night Stalker Richard Ramirez committed his first murder in June 1984. His victim was a 79-year-old woman who was stabbed repeatedly and sexually assaulted and then had her throat slashed. It would be eight months before Ramirez murdered again. In the spring, Ramirez began a murderous rampage that resulted in 13 ad- ditional killings and 5 rapes.

His modus operandi was to enter a home through an open window, shoot the male residents, and savagely rape his female vic- tims. He scribed a pentagram on the wall of one of his victims and the words Jack the Knife, and was reported by another to force her to “swear to Satan” during the assault. His identity still unknown, the news media dubbed him the “Night Stalker.” As the body count continued to rise, public hysteria and a media frenzy prevailed.

The break in the case came when the license plate of what seemed to be a suspicious car related to a sighting of the Night Stalker was reported to the police. The police determined that the car had been stolen and eventually located it, abandoned in a parking lot. After processing the car for prints, police found one usable partial fingerprint. This fingerprint was entered into the Los Angeles Police Department’s brand-new AFIS comput- erized fingerprint system.

The Night Stalker was identified as Richard Ramirez, who had been fingerprinted following a traffic violation some years before. Police searching the home of one of his friends found the gun used to commit the murders, and jewelry belonging

to his victims was found in the possession of Ramirez’s sister. Ramirez was convicted of murder and sentenced to death in 1989.

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crime-scene prints: visible prints are made by fingers touching a surface after the ridges have been in contact with a colored material such as blood, paint, grease, or ink; plastic prints are ridge impressions left on a soft material such as putty, wax, soap, or dust; and latent or invisible prints are impressions caused by the transfer of body perspiration or oils present on finger ridges to the surface of an object.

Locating Fingerprints Locating visible or plastic prints at the crime scene normally presents little problem to the inves- tigator because these prints are usually distinct and visible to the eye. Locating latent or invisible

The Mayfield Affair On March 11, 2004, a series of ten explosions at four sites oc- curred on commuter trains traveling to or near the Atocha train station in Madrid, Spain. The death toll from these explosions was nearly 200, with more than 1,500 injured. On the day of the attack, a plastic bag was found in a van previously reported as stolen. The bag contained copper detonators like those used on the train bombs. On March 17, the FBI received electronic images of latent fingerprints that were recovered from the plas- tic bag. A search was initiated on the FBI’s IAFIS. A senior fingerprint examiner encoded seven minutiae points from the high-resolution image of one suspect latent fingerprint and ini- tiated an IAFIS search matching the print to Brandon Mayfield.

Mayfield’s prints were in the FBI’s central database because they had been taken when he joined the military, where he served for eight years before being honorably dis- charged as a second lieutenant. After a visual comparison of the suspect and file prints, the examiner concluded a “100 percent match.” The identification was verified by a retired FBI fingerprint examiner with more than 30 years of experience who was under contract with the bureau, as well as by a court-appointed independent fingerprint examiner (see figure).

Mayfield, age 37, a Muslim convert, was arrested on May 6 on a material witness warrant. The U.S. Attorney’s Of- fice came up with a list of Mayfield’s potential ties to Muslim terrorists, which they included in the affidavit they presented to the federal judge who ordered his arrest and detention. The document also said that, although no travel records were found for Mayfield, “It is believed that Mayfield may have traveled under a false or fictitious name.” On May 24, after the Span- iards had linked the print from the plastic bag to an Algerian national, Mayfield’s case was thrown out. The FBI issued him a highly unusual official apology, and his ordeal became a stun- ning embarrassment to the U.S. government.

The Mayfield incident has also been the subject of an investigation by the Office of the Inspector General (OIG), U.S. Department of Justice (http://www.usdoj.gov/oig/special/ s0601/final.pdf). The OIG investigation concluded that a “se- ries of systemic issues” in the FBI laboratory contributed to the Mayfield misidentification. The report noted that the FBI has made significant procedural modifications to help prevent similar errors in the future and strongly supported the FBI’s decision to undertake research to develop more objective stan- dards for fingerprint identification.

The impact of the Mayfield affair on fingerprint technol- ogy as currently practiced and the weight courts will assign to fingerprint matches remain open questions.

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(a) Questioned print recovered in connection with the Madrid bombing investigation. (b) File print of Brandon Mayfield.

visible print A fingerprint made when the finger deposits a visible material such as ink, dirt, or blood onto a surface.

plastic print A fingerprint impressed in a soft surface.

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prints is obviously much more difficult and requires the use of techniques to make the print vis- ible. Although the investigator can choose from several methods for visualizing a latent print, the choice depends on the type of surface being examined.

Hard and nonabsorbent surfaces (such as glass, mirror, tile, and painted wood) require dif- ferent development procedures from surfaces that are soft and porous (such as papers, cardboard, and cloth). Prints on the former are preferably developed by the application of a powder or treat- ment with superglue, whereas prints on the latter generally require treatment with one or more chemicals.

Sometimes the most difficult aspect of fingerprint examination is the location of prints. Re- cent advances in fingerprint technology have led to the development of an ultraviolet image con- verter for the purpose of detecting latent fingerprints. This device, called the Reflected Ultraviolet Imaging System (RUVIS), can locate prints on most nonabsorbent surfaces without the aid of chemical or powder treat- ments (see Figure 6–11).

RUVIS detects the print in its natural state by aiming UV light at the surface suspected of containing prints. When the UV light strikes the fingerprint, the light is reflected back to the viewer, differentiating the print from its background surface. The transmitted UV light is then con- verted into visible light by an image intensifier. Once the print is located in this manner, the crime-scene investigator can develop it in the most appropriate fashion (see Figure 6–12).

Developing Latent Prints FINGERPRINT POWDERS Fingerprint powders are commercially available in a variety of compositions and colors. These powders, when applied lightly to a nonabsorbent surface with a camel’s-hair or fiberglass brush, readily adhere to perspiration residues and/or deposits of body oils left on the surface (see Figure 6–13).

Experienced examiners find that gray and black powders are ad- equate for most latent-print work; the examiner selects the powder that affords the best color contrast with the surface being dusted. Hence, the gray powder, composed of an aluminum dust, is used on dark-colored surfaces. It is also applied to mirrors and metal surfaces that are polished to a mirrorlike finish because these surfaces photograph as black. The black powder, composed basically of black carbon or charcoal, is ap- plied to white or light-colored surfaces.

Other types of powders are available for developing latent prints. A magnetic-sensitive powder can be spread over a surface with a

FIGURE 6–11 A Reflected Ultraviolet Imaging System allows an investigator to directly view surfaces for the presence of untreated latent fingerprints.

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FIGURE 6–12 Using a Reflected Ultraviolet Imaging System with the aid of a UV lamp to search for latent fingerprints.

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magnet in the form of a Magna Brush. A Magna Brush does not have any bristles to come in contact with the surface, so there is less chance that the print will be destroyed or dam- aged. The magnetic-sensitive powder comes in black and gray and is especially useful on such items as finished leather and rough plastics, where the minute texture of the surface tends to hold particles of ordinary powder. Fluorescent pow- ders are also used to develop latent fingerprints. These pow- ders fluoresce under ultraviolet light. By photographing the fluorescence pattern of the developing print under UV light, it is possible to avoid having the color of the surface obscure the print.

IODINE FUMING Of the several chemical methods used for visualizing latent prints, iodine fuming is the oldest. Iodine is a solid crystal that, when heated, is transformed into a vapor without passing through a liquid phase; such a transformation is called sublimation. Most often, the suspect material is placed in an enclosed cabinet along with iodine crystals (see Figure 6–14). As the crystals are heated, the resultant vapors fill the chamber and combine with constituents of the latent print to make it visible. The reasons why latent prints are visualized by iodine vapors are not yet fully

understood. Many believe that the iodine fumes combine with fatty oils; however, there is also convincing evidence that the iodine may actually interact with residual water left on a print from perspiration.2

Unfortunately, iodine prints are not permanent and begin to fade once the fuming process is stopped. Therefore, the examiner must photograph the prints immediately on development in order to retain a permanent record. However, if the developed print is simply covered with a clear cellophane tape soon after development, will be usable for at least several months. Also, iodine- developed prints can be fixed with a 1 percent solution of starch in water, applied by spraying. The print turns blue and lasts for several weeks to several months.

NINHYDRIN Another chemical used for visualizing latent prints is ninhydrin. The development of latent prints with ninhydrin depends on its chemical reaction to form a purple-blue color with amino acids present in trace amounts in perspiration. Ninhydrin (triketohydrindene hydrate) is commonly sprayed onto the porous surface from an aerosol can. A solution is prepared by mixing the ninhydrin powder with a suitable solvent, such as acetone or ethyl alcohol; a 0.6 percent solution appears to be effective for most applications.

Generally, prints begin to appear within an hour or two after ninhydrin application; however, weaker prints may be visualized after 24 to 48 hours. The development can be hastened if the treated specimen is heated in an oven or on a hot plate at a temperature of 80–100°C. The ninhy- drin method has developed latent prints on paper as old as 15 years.

PHYSICAL DEVELOPER Physical Developer is a third chemical mixture used for visualizing latent prints. Physical Developer is a silver nitrate–based liquid reagent. The procedure for preparing and using Physical Developer is described in Appendix IV. This method has gained wide acceptance by fingerprint examiners, who have found it effective for visualizing latent prints that remain undetected by the previously described methods. Also, this technique is effective for developing latent fingerprints on porous articles that may have been wet at one time.

For most fingerprint examiners, the chemical method of choice is ninhydrin. Its extreme sensitivity and ease of application have all but eliminated the use of iodine for latent-print visu- alization. However, when ninhydrin fails, development with Physical Developer may provide identifiable results. Application of Physical Developer washes away any traces of proteins from an object’s surface; hence, if one wishes to use all of the previously mentioned chemical

FIGURE 6–13 Developing a latent fingerprint on a surface by apply- ing a fingerprint powder with a fiberglass brush.

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2 J. Almag, Y. Sasson, and A. Anati, “Chemical Reagents for the Development of Latent Fingerprints II: Controlled Addi- tion of Water Vapor to Iodine Fumes—A Solution to the Aging Problem,” Journal of Forensic Sciences 24 (1979): 431.

iodine fuming A technique for visualizing latent fingerprints by exposing them to iodine vapors.

sublimation A physical change from the solid directly into the gaseous state.

ninhydrin A chemical reagent used to de- velop latent fingerprints on porous materials by reacting with amino acids in perspiration.

Physical Developer A silver nitrate–based reagent for- mulated to develop latent finger- prints on porous surfaces.

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development methods on the same surface, it is necessary to first fume with iodine, follow this treatment with ninhydrin, and then apply Physical Developer to the object.

SUPERGLUE FUMING In the past, chemical treatment for fingerprint development was reserved for porous surfaces such as paper and cardboard. However, since 1982, a chemical technique known as superglue fuming has gained wide popularity for developing latent prints on nonporous surfaces such as metals, electrical tape, leather, and plastic bags (see Figure 6–15).3

Superglue is approximately 98–99 percent cyanoacrylate ester, a chemical that interacts with and visualizes a latent fingerprint. Cyanoacrylate ester fumes can be created when superglue is placed on absorbent cotton treated with sodium hydroxide. The fumes can also be created by heating the glue. The fumes and the evidential object are contained within an enclosed chamber for up to six hours. Development occurs when fumes from the glue adhere to the latent print, usually producing a white-appearing latent print. Interestingly, small enclosed areas, such as the interior of an automobile, have been successfully processed for latent prints with fumes from superglue.

Through the use of a small handheld wand, cyanoacrylate fuming is now easily done at a crime scene or in a laboratory setting. The wand heats a small cartridge containing cyanoacry- late. Once heated, the cyanoacrylate vaporizes, allowing the operator to direct the fumes onto the suspect area (see Figure 6–16).

OTHER TECHNIQUES FOR VISUALIZATION One of the most exciting and dynamic areas of research in forensic science today is the application of chemical techniques to the visualization of latent fingerprints. Changes are occurring rapidly as researchers uncover a variety of processes applicable to the visualization of latent fingerprints. Interestingly, for many years progress in this

FIGURE 6–14 A heated fuming cabinet.

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FIGURE 6–15 Superglue fuming a nonporous metallic surface in the search for latent fingerprints.

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3 F. G. Kendall and B. W. Rehn, “Rapid Method of Superglue Fuming Application for the Development of Latent Fingerprints,” Journal of Forensic Sciences 28 (1983): 777.

superglue fuming A technique for visualizing latent fingerprints on nonporous surfaces by exposing them to cyanoacrylate vapors; named for the commercial product Super Glue.

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field was minimal, and fingerprint specialists traditionally relied on three chemical techniques— iodine, ninhydrin, and silver nitrate—to reveal a hidden fingerprint. Then superglue fuming extended chemical development to prints deposited on nonporous surfaces.

(a)

FIGURE 6–16 (a) A handheld fuming wand uses disposable cartridges containing cyanoacrylate. The wand is used to develop prints at the crime scene and (b) in the laboratory.

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wearer. The filter also protects the operator against eye damage from scattered or reflected laser light. Likewise, latent-print residue producing sufficient flu- orescence can be photographed by placing this same filter across the lens of the camera. Examination of specimens and photography of the fluorescing latent prints are carried out in a darkened room.

Fluorescence

The first hint of things to come was the discovery that latent fingerprints could be visualized by exposure to laser light. This laser method took advantage of the fact that perspiration contains a variety of components that fluoresce when illuminated by laser light. Fluorescence occurs when a substance absorbs light and reemits the light in wavelengths longer than the illuminating source. Importantly, substances that emit light or fluo- resce are more readily seen with either the naked eye or through photography than are non-light-emitting materials. The high sensitivity of fluorescence serves as the underlying principle of many of the new chemical techniques used to visualize latent fingerprints.

The earliest use of fluorescence to visualize fin- gerprints came with the direct illumination of a fin- gerprint with argon–ion lasers. This laser type was chosen because its blue-green light output induced some of the perspiration components of a fingerprint to fluoresce (see figure). The major drawback of this approach is that the perspiration components of a fingerprint are often present in quantities too minute to observe even with the aid of fluorescence. The fin- gerprint examiner, wearing safety goggles containing optical filters, visually examines the specimen being exposed to the laser light. The filters absorb the laser light and permit the wavelengths at which latent-print residues fluoresce to pass through to the eyes of the

inside the science Directional mirror Laser

Dispersal lens

Barrier filter Observer

Schematic depicting latent-print detection with the aid of a laser. A fingerprint examiner, wearing safety goggles containing optical filters, examines the specimen being exposed to the laser light. The filter absorbs the laser light and permits the wavelengths at which latent-print resi- dues fluoresce to pass through to the eyes of the wearer.

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fluoresce To emit visible light when exposed to light of a shorter wavelength.

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The next advancement in latent-fingerprint develop- ment occurred with the discovery that fingerprints could be treated with chemicals that would induce fluorescence when exposed to laser illumination. For example, the application of zinc chloride after ninhydrin treatment or the applica- tion of the dye rhodamine 6G after superglue fuming caused fluorescence and increased the sensitivity of detection on exposure to laser illumination. The discovery of numerous chemical developers for visualizing fingerprints through fluorescence quickly followed. This knowledge set the stage for the next advance in latent-fingerprint development—the alternate light source.

With the advent of chemically induced fluorescence, lasers were no longer needed to induce fingerprints to fluo- resce through their perspiration residues. High-intensity light sources or alternate light sources have proliferated and all but replaced laser lights (see Figure 6–17). High-intensity quartz halogen or xenon-arc light sources can be focused on a sus- pect area through a fiber-optic cable. This light can be passed through several filters, giving the user more flexibility in se- lecting the wavelength of light to be aimed at the latent print. Alternatively, lightweight, portable alternate light sources that use light-emitting diodes (LEDs) are also commercially available (see Figure 6–18). In most cases, these light sources have proven to be as effective as laser light in developing latent prints, and they are commercially available at costs sig- nificantly less than those of laser illuminators. Furthermore, these light sources are portable and can be readily taken to any crime scene.

NEWER CHEMICAL PROCESSES A large number of chemical treatment processes are available to the fingerprint examiner, and the field is in a constant state of flux. Selection of an appropriate procedure is best left to technicians who have developed their skills through casework experience.

Newer chemical processes include a substitute for nin- hydrin called DFO (1,8-diazafluoren-9-one). This chemical visualizes latent prints on porous materials when exposed to an alternate light source. DFO has been shown to develop 2.5 times as many latent prints on paper as ninhydrin. A chem- ical called 1,2-indanedione is also emerging as a potential reagent for the development of latent fingerprints on porous surfaces. 1,2-indanedione gives both good initial color and strong fluorescence when reacted with amino acids derived from prints and thus has the potential to provide in one pro- cess what ninhydrin and DFO can do in two different steps.

Dye combinations known as RAM, RAY, and MRM 10, when used in conjunction with superglue fuming, have been effective in visualizing latent fingerprints by fluorescence. A number of chemical formulas use- ful for latent-print development are listed in Appendix IV.

Studies have demonstrated that common fingerprint-developing agents do not interfere with DNA- testing methods used for characterizing bloodstains.4 Nonetheless, in cases involving items with material

4 C. Roux et al., “A Further Study to Investigate the Effect of Fingerprint Enhancement Techniques on the DNA Analy- sis of Bloodstains,” Journal of Forensic Identification 49 (1999): 357; C. J. Frégeau et al., “Fingerprint Enhancement Revisited and the Effects of Blood Enhancement Chemicals on Subsequent Profiler Plus™ Fluorescent Short Tandem Repeat DNA Analysis of Fresh and Aged Bloody Fingerprints,” Journal of Forensic Sciences 45 (2000): 354; and P. Grubwieser et al., “Systematic Study on STR Profiling on Blood and Saliva Traces after Visualization of Finger- prints,” Journal of Forensic Sciences 48 (2003): 733.

FIGURE 6–18 Lightweight handheld alternate light source that uses an LED light source.

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FIGURE 6–17 An alternate light source system incorporating a high-intensity light source.

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adhering to their surfaces and/or items that will require further laboratory examinations, fingerprint pro- cessing should not be performed at the crime scene. Rather, the items should be submitted to the labora- tory, where they can be processed for fingerprints in conjunction with other necessary examinations.

Preservation of Developed Prints Once the latent print has been visualized, it must be permanently preserved for future comparison and possible use in court as evidence. A photograph must be taken before any further attempts at preservation. Any camera equipped with a close-up lens will do; however, many investigators prefer to use a camera specially designed for fingerprint photography. Such a camera comes equipped with a fixed focus to take photographs on a 1:1 scale when the camera’s open eye is held exactly flush against the print’s surface (see Figure 6–19). In addition, photographs must be taken to pro- vide an overall view of the print’s location with respect to other evidential items at the crime scene.

Once photographs have been secured, one of two procedures is to be followed. If the ob- ject is small enough to be transported without destroying the print, it should be preserved in its entirety; the print should be covered with cellophane so it will be protected from damage. On the other hand, prints on large immovable objects that have been developed with a powder can best be preserved by “lifting.” The most popular type of lifter is a broad adhesive tape similar to clear adhesive tape. When the powdered surface is covered with the adhesive side of the tape and pulled up, the powder is transferred to the tape. Then the tape is placed on a properly labeled card that provides a good background contrast with the powder.

A variation of this procedure is the use of an adhesive-backed clear plastic sheet attached to a colored cardboard backing. Before it is applied to the print, a celluloid separator is peeled from the plastic sheet to expose the adhesive lifting surface. The tape is then pressed evenly and firmly over the powdered print and pulled up (see Figure 6–20). The sheet containing the adhering pow- der is now pressed against the cardboard backing to provide a permanent record of the fingerprint.

Digital Imaging for Fingerprint Enhancement When fingerprints are lifted from a crime scene, they are not usually in perfect condition, making the analysis that much more difficult. Computers have advanced technology in most fields, and

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FIGURE 6–19 Camera fitted with an adapter designed to give an approximate 1:1 photo- graph of a fingerprint.

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fingerprint identification has not been left behind. With the help of digital imaging software, fingerprints can now be en- hanced for the most accurate and comprehensive analysis.

Creating Digital Images Digital imaging is the process by which a picture is converted into a digital file. The image produced from this digital file is composed of numerous square electronic dots called pixels. Images composed of only black and white elements are re- ferred to as grayscale images. Each pixel is assigned a number according to its intensity. The grayscale image is made from the set of numbers to which a pixel may be assigned, rang- ing from 0 (black) to 255 (white). Once an image is digitally stored, it is manipulated by computer software that changes the numerical value of each pixel, thus altering the image as directed by the user. Resolution reveals the degree of detail that can be seen in an image. It is defined in terms of dimen- sions, such as 800 × 600 pixels. The larger the numbers, the more closely the digital image re- sembles the real-world image.

The input of pictures into a digital imaging system is usually done through the use of scan- ners, digital cameras, and video cameras. After the picture is changed to its digital image, several methods can be employed to enhance the image. The overall brightness of an image, as well as the contrast between the image and the background, can be adjusted through contrast-enhancement methods. One approach used to enhance an image is spatial filtering. Several types of filters produce various effects. A low-pass filter is used to eliminate harsh edges by reducing the intensity differ- ence between pixels. A second filter, the high-pass filter, operates by modifying a pixel’s numerical value to exaggerate its intensity difference from that of its neighbor. The resulting effect increases the contrast of the edges, thus providing a high contrast between the elements and the background.

Analyzing Digital Images Frequency analysis, also referred to as frequency Fourier transform (FFT), is used to identify periodic or repetitive patterns such as lines or dots that interfere with the interpretation of the image. These patterns are diminished or eliminated to enhance the appearance of the image. Interestingly, the spacings between fingerprint ridges are themselves periodic. Therefore, the contribution of the fingerprint can be identified in FFT mode and then enhanced. Likewise, if ridges from overlapping prints are positioned in different directions, their corresponding fre- quency information is at different locations in FFT mode. The ridges of one latent print can then be enhanced while the ridges of the other are suppressed.

Color interferences also pose a problem when analyzing an image. For example, a latent fingerprint found on paper currency or a check may be difficult to analyze because of the dis- tracting colored background. With the imaging software, the colored background can simply be removed to make the image stand out (see Figure 6–21). If the image itself is a particular color, such as a ninhydrin-developed print, the color can be isolated and enhanced to distinguish it from the background.

Digital imaging software also provides functions in which portions of the image can be examined individually. With a scaling and resizing tool, the user can select a part of an image and resize it for a closer look. This function operates much like a magnifying glass, helping the examiner view fine details of an image.

An important and useful tool, especially for fingerprint identification, is the compare func- tion. This specialized feature places two images side by side and allows the examiner to chart the common features on both images simultaneously (see Figure 6–22). The zoom function is used in conjunction with the compare tool. As the examiner zooms into a portion of one image, the software automatically zooms into the second image for comparison.

Although digital imaging is undoubtedly an effective tool for enhancing and analyzing im- ages, it is only as useful as the images it has to work with. If the details do not exist on the original images, the enhancement procedures are not going to work. The benefits of digital enhancement methods are apparent when weak images are made more distinguishable.

FIGURE 6–20 “Lifting” a fingerprint.

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digital imaging A process through which a picture is converted into a series of square electronic dots known as pixels; the picture is manipulated by com- puter software that changes the numerical value of each pixel.

pixel A square electronic dot that is used to compose a digital image.

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chapter summary Fingerprints are a reproduction of friction skin ridges found on the palm side of the fingers and thumbs. The ba- sic principles underlying the use of fingerprints in crimi- nal investigations are that (1) a fingerprint is an individual characteristic because no two fingers have yet been found to possess identical ridge characteristics, (2) a fingerprint remains unchanged during an individual’s lifetime, and (3) fingerprints have general ridge patterns that permit them to be systematically classified. All fingerprints are divided

into three classes on the basis of their general pattern: loops, whorls, and arches.

Fingerprint classification systems are based on knowl- edge of fingerprint pattern classes. The individuality of a fin- gerprint is not determined by its general shape or pattern, but by a careful study of its ridge characteristics. The expert must demonstrate a point-by-point comparison in order to prove the identity of an individual. AFIS aids this process by converting the image of a fingerprint into digital minutiae that contain data

FIGURE 6–22 Current imaging software allows fingerprint analysts to prepare a fingerprint comparison chart. The fingerprint examiner can compare prints side by side and display important features that are consis- tent between the finger- prints. The time needed to create a display of this sort digitally is about 30 to 60 minutes.

FIGURE 6–21 A fingerprint being en- hanced in Adobe Photo- shop. In this example, on the left is the original scan of an inked fingerprint on a check. On the right is the same image after using Adobe Photoshop’s Chan- nel Mixer to eliminate the green security background.

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showing ridges at their points of termination (ridge endings) and their branching into two ridges (bifurcations). A single fin- gerprint can be searched against the FBI AFIS digital database of 50 million fingerprint records in a matter of minutes.

Once the finger touches a surface, perspiration, along with oils that may have been picked up by touching the hairy por- tions of the body, is transferred onto that surface, thereby leav- ing an impression of the finger’s ridge pattern (a fingerprint). Prints deposited in this manner are invisible to the eye and are commonly referred to as latent or invisible fingerprints.

Visible prints are made when fingers touch a surface after the ridges have been in contact with a colored material such as blood, paint, grease, or ink. Plastic prints are ridge impressions left on a soft material, such as putty, wax, soap, or dust. Latent prints depos- ited on hard and nonabsorbent surfaces (such as glass, mirror, tile, and painted wood) are preferably developed by the application of a powder; prints on porous surfaces (such as paper and cardboard) generally require treatment with a chemical. Examiners use various

chemical methods to visualize latent prints, such as iodine fuming, ninhydrin, and Physical Developer. Superglue fuming develops la- tent prints on nonporous surfaces, such as metals, electrical tape, leather, and plastic bags. Development occurs when fumes from the glue adhere to the print, usually producing a white latent print.

The high sensitivity of fluorescence serves as the under- lying principle of many of the new chemical techniques used to visualize latent fingerprints. Fingerprints are treated with chemicals that induce fluorescence when exposed to a high- intensity light or an alternate light source.

Once the latent print has been visualized, it must be per- manently preserved for future comparison and for possible use as court evidence. A photograph must be taken before any fur- ther attempts at preservation are made. If the object is small enough to be transported without destroying the print, it should be preserved in its entirety. Prints on large immovable objects that have been developed with a powder are best preserved by “lifting” with a broad adhesive tape.

1. The first systematic attempt at personal identification was devised and introduced by ___________.

2. A system of identification relying on precise body mea- surements is known as ___________.

3. The fingerprint classification system used in most Eng- lish-speaking countries was devised by ___________.

4. True or False: The first systematic and official use of fingerprints for personal identification in the United States was adopted by the New York City Civil Service Commission.___________

5. The individuality of a fingerprint (is, is not) determined by its pattern.

6. A point-by-point comparison of a fingerprint’s ___________ must be demonstrated in order to prove identity.

7. ___________ are a reproduction of friction skin ridges.

8. The form and pattern of skin ridges are determined by the (epidermis, dermal papillae).

9. A permanent scar forms in the skin only when an injury damages the ___________.

10. Fingerprints (can, cannot) be changed during a person’s lifetime.

11. The three general patterns into which fingerprints are di- vided are ___________, ___________, and ___________.

12. The most common fingerprint pattern is the ___________.

13. Approximately 5 percent of the population has the ___________ fingerprint pattern.

14. A loop pattern that opens toward the thumb is known as a(n) (radial, ulnar) loop.

15. The pattern area of the loop is enclosed by two diverg- ing ridges known as ___________.

16. The ridge point nearest the type-line divergence is known as the ___________.

17. All loops must have (one, two) delta(s).

18. The approximate center of a loop pattern is called the ___________.

19. If an imaginary line drawn between the two deltas of a whorl pattern touches any of the spiral ridges, the pat- tern is classified as a (plain whorl, central pocket loop).

20. The simplest of all fingerprint patterns is the ___________.

21. Arches (have, do not have) type lines, deltas, and cores.

22. ACE-V is an acronym for a four step process: ___________, ___________, ___________, and ___________.

23. True or False: Level 2 details cannot individualize a fingerprint.

24. The presence or absence of the ___________ pattern is used as a basis for determining the primary classifica- tion in the Henry system.

25. The largest category (25 percent) in the primary clas- sification system is (1/1, 1/2).

26. A fingerprint classification system (can, cannot) un- equivocally identify an individual.

27. True or False: Computerized fingerprint search systems match prints by comparing the position of bifurcations and ridge endings. ___________

28. A fingerprint left by a person with soiled or stained fin- gertips is called a(n) ___________.

29. ___________ fingerprints are impressions left on a soft material.

30. Fingerprint impressions that are not readily visible are called ___________.

31. Fingerprints on hard and nonabsorbent surfaces are best developed by the application of a(n) ___________.

32. Fingerprints on porous surfaces are best developed with ___________ treatment.

review questions

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33. ___________ vapors chemically combine with fatty oils or residual water to visualize a fingerprint.

34. The chemical ___________ visualizes fingerprints by its reaction with amino acids.

35. Chemical treatment with ___________ visualizes finger- prints on porous articles that may have been wet at one time.

36. True or False: A latent fingerprint is first treated with Physical Developer followed by ninhydrin. ___________

37. A chemical technique known as ___________ is used to develop latent prints on nonporous surfaces such as metal and plastic.

38. ___________ occurs when a substance absorbs light and reemits the light in wavelengths longer than the il- luminating source.

39. High-intensity light sources known as ___________ are effective in developing latent fingerprints.

40. Once a fingerprint has been visualized, it must be pre- served by ___________.

41. The image produced from a digital file is composed of numerous square electronic dots called ___________.

42. A (high-pass filter, frequency Fourier transform analy- sis) is used to identify repetitive patterns such as lines or dots that interfere with the interpretation of a digi- tized fingerprint image.

application and critical thinking

1. Classify each of the prints shown in the figure as loop, whorl, or arch.

(1). (2).

(5). (6).

(3). (4).

2. A description of the types of prints from the fingers of a criminal suspect appears below. Using the FBI system, determine the primary classification of this individual.

Finger Right Hand Left Hand

Thumb Whorl Whorl

Index Loop Whorl

Middle Whorl Arch

Ring Whorl Whorl

Little Arch Whorl

3. While searching a murder scene, you find the following items that you believe may contain latent fingerprints. Indicate whether prints on each item should be devel- oped using fingerprint powder or chemicals.

a. A leather sofa

b. A mirror

c. A painted wooden knife handle

d. Blood-soaked newspapers

e. A revolver

4. Criminalist Frank Mortimer is using digital imaging to enhance latent fingerprints. Indicate which features of digital imaging he would most likely use for each of the following tasks:

a. Isolating part of a print and enlarging it for closer examination

b. Increasing the contrast between a print and the background surface on which it is located

c. Examining two prints that overlap one another

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7. At the Museum of Culture Studies, a diary that belonged to Martin Luther King, Jr., has been stolen and replaced by a fake. The only evidence is a fingerprint impression left by the thief on the fake diary. The police suspects four individuals who have had previous criminal records for similar crimes. Their fingerprints already exist in the police database. KJ, Ivan, Lisa, and Charlie are the four suspects. Carefully examine the criminal’s finger- print impression and identify the suspect fingerprint that matches with it.

5. The following are fingerprint patterns of three men and a woman with criminal records for robbery. Identify the following fingerprints according to the three groups and the subgroups of fingerprints.

Ivan Lisa

Charlie

further references

U.S. Department of Justice, The Fingerprint Sourcebook, http://www.OJP.usdoj.gov/nij/pubs-sum/225320.htm.

Komarinski, Peter, Automated Fingerprint Identification Systems (AFIS). Burlington, Mass.: Elsevier Academic Press, 2004.

Ramotowski, R., ed., Lee and Gaensleen’s Advances in Fingerprint Technology, 3rd ed. Boca Raton, Fla.: CRC Press, 2012.

6. Count the number of bifurcations in the following prints. Choose between 9, 11, and 13 as the number of bifurcations:

Crime Scene Fingerprint

KJ Inan

Lisa Charlie

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The Lindbergh Baby Case

headline news

On the evening of March 1, 1932, a kidnapper crept up his homemade ladder and stole the baby of Charles and Anne Lindbergh directly from the second-floor nursery of their house in Hopewell, New Jersey. The only evidence of his coming was a ransom note, the ladder, a chisel, and the tragic absence of the infant. A couple of months later, though the $50,000 ransom had been paid, the baby turned up dead in the woods a mile away. There was no additional sign of the killer. Fortunately, when finally studied by wood technologist Arthur Koehler, the abandoned ladder yielded some important investigative clues.

By studying the types of wood used and the cutter marks on the wood, Koehler ascertained where the materials might have come from and what specific equipment was used to create them. Koehler traced the wood from a South Carolina mill to a lumberyard in the Bronx, New York. Unfortunately the trail went cold, as the lumberyard did not keep sales records of purchases. The break in the case came in 1934, when Bruno Richard

Hauptmann paid for gasoline with a bill that matched a serial number on the ransom money. Koehler

showed that microscopic markings on the wood were made by a tool in Hauptmann’s possession. Ultimately, handwriting analysis of the ransom note clearly

showed it to be written by Hauptmann.

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After studying this chapter you should be able to:

the microscope

binocular condenser depth of focus eyepiece lens field of view microspectrophotometer monocular objective lens parfocal plane-polarized light polarizer real image transmitted

illumination vertical or reflected

illumination virtual image

KEY TERMS

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150 CHAPTER 7

Basics of the Microscope A microscope is an optical instrument that uses a lens or a combination of lenses to mag- nify and resolve the fine details of an object. The earliest methods for examining physical evidence in crime laboratories relied almost solely on the microscope to study the structure and composition of matter. Even the advent of modern analytical instrumentation and tech- niques has done little to diminish the usefulness of the microscope for forensic analysis. If anything, the development of the powerful scanning electron microscope promises to add a new dimension to forensic science heretofore unattainable within the limits of the ordinary light microscope.

The earliest and simplest microscope was the single lens commonly referred to as a magnify- ing glass. The handheld magnifying glass makes things appear larger than they are because of the way light rays are refracted, or bent, in passing from the air into the glass and back into the air. The magnified image is observed by looking through the lens, as shown in Figure 7–1. Such an image is known as a virtual image; it can be seen only by looking through a lens and cannot be viewed directly. This is distinguished from a real image, which can be seen directly, like the image that is projected onto a motion picture screen.

The ordinary magnifying glass can achieve a magnification of about 5 to 10 times. Higher magnifying power is obtainable only with a compound microscope, constructed of two lenses mounted at each end of a hollow tube. The object to be magnified is placed under the lower lens, called the objective lens, and the magnified image is viewed through the upper lens, known as the eyepiece lens. As shown in Figure 7–2, the objective lens forms a real, inverted, magnified image of the object. The eyepiece, acting just like a simple magni- fying glass, further magnifies this image into a virtual image, which is what is seen by the eye. The combined magnifying power of both lenses can produce an image magnified up to 1,500 times.

The optical principles of the compound microscope are incorporated into the basic design of different types of light microscopes. The microscopes most applicable for examining forensic specimens are as follows:

1. The compound microscope 2. The comparison microscope 3. The stereoscopic microscope 4. The polarizing microscope 5. The microspectrophotometer

After describing these five microscopes, we will talk about a completely different approach to microscopy, the scanning electron microscope (SEM). This instrument focuses a beam of electrons, instead of visible light, onto the specimen to produce a magnified image. The principle and design of this microscope permit magnifying powers as high as 100,000 times.

virtual image An image that cannot be seen directly. It can be seen only by a viewer looking through a lens.

Virtual image

Object

Lens Eye

real image An image formed by the actual convergence of light rays on a screen.

objective lens The lower lens of a microscope, which is positioned directly over the specimen.

eyepiece lens The lens of a microscope into which the viewer looks; same as the ocular lens.

FIGURE 7–1 The passage of light through a lens, showing how magnification is obtained.

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The Compound Microscope The parts of the compound microscope are illustrated in Figure 7–3. Basically, this microscope consists of a mechanical system, which supports the microscope, and an optical system. The optical system illuminates the object under investigation and passes the light through a series of lenses to form an image of the specimen on the retina of the eye. The optical path of light through a compound microscope is shown in Figure 7–4.

Parts of the Compound Microscope The mechanical system of the compound microscope is composed of six parts:

Base (1). The support on which the instrument rests. Arm (2). A C-shaped upright structure, hinged to the base, that supports the microscope and

acts as a handle for carrying. Stage (3). The horizontal plate on which the specimens are placed for study. The specimens are

normally mounted on glass slides that are held firmly in place on the stage by spring clips. Body tube (4). A cylindrical hollow tube on which the objective and eyepiece lenses are

mounted at opposite ends. This tube merely serves as a corridor through which light passes from one lens to another.

Coarse adjustment (5). This knob focuses the microscope lenses on the specimen by raising and lowering the body tube.

Fine adjustment (6). The movements effected by this knob are similar to those of the coarse adjustment but are of a much smaller magnitude.

The optical system is made up of four parts: Illuminator (7). Most modern microscopes use artificial light supplied by a lightbulb to illu-

minate the specimen being examined. If the specimen is transparent, the light is directed up toward and through the specimen stage from an illuminator built into the base of the micro- scope. This is known as transmitted illumination. When the object is opaque—that is, not transparent—the light source must be placed above the specimen so that it can reflect off the specimen’s surface and into the lens system of the microscope. This type of illumination is known as vertical or reflected illumination.

Eyepiece

Real image formed by objective

Eye

Object

Objective

Virtual image seen by eye

Light source

FIGURE 7–2 The principle of the compound microscope. The passage of light through two lenses forms the virtual image of the object seen by the eye.

transmitted illumination Light that passes up from the con- denser and through the specimen.

vertical or reflected illumination Illumination of a specimen from above; in microscopy it is used to examine opaque specimens.

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FIGURE 7–3 Parts of the compound microscope: (1) base, (2) arm, (3) stage, (4) body tube, (5) coarse adjust, (6) fine adjust, (7) illuminator, (8) condenser, (9) objective lens, and (10) eyepiece lens.

FIGURE 7–4 Optics of the compound microscope.

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Condenser (8). The condenser collects light rays from the base illuminator and concentrates them on the specimen. The simplest condenser is known as the Abbé condenser. It consists of two lenses held together in a metal mount. The condenser also includes an iris diaphragm that can be opened or closed to control the amount of light passing into the condenser.

Objective lens (9). This is the lens positioned closest to the specimen. To facilitate changing from one objective lens to another, several objectives are mounted on a revolving nosepiece or turret located above the specimen. Most microscopes are parfocal, meaning that when the microscope is focused with one objective in position, the other objective can be rotated into place by revolving the nosepiece while the specimen remains very nearly in correct focus.

Eyepiece or ocular lens (10). This is the lens closest to the eye. A microscope with only one eyepiece is monocular; one constructed with two eyepieces (one for each eye) is binocular.

Properties of the Compound Microscope Each microscope lens is inscribed with a number signifying its magnifying power. The im- age viewed by the microscopist will have a total magnification equal to the product of the magnifying power of the objective and eyepiece lenses. For example, an eyepiece lens with a magnification of 103 used in combination with an objective lens of 103 has a total magnifica- tion power of 1003. Most forensic work requires a 103 eyepiece in combination with either a 43, 103, 203, or 453 objective. The respective magnifications will be 403, 1003, 2003, and 4503.

In addition, each objective lens is inscribed with its numerical aperture (N.A.). The ability of an objective lens to resolve details into separate images instead of one blurred image is directly proportional to the numerical aperture value of the objective lens. For example, an objective lens of N.A. 1.30 can separate details at half the distance of a lens with an N.A. of 0.65. The maximum useful magnification of a compound microscope is approximately 1,000 times the N.A. of the objective being used. This magnification is sufficient to permit the eye to see all the detail that can be resolved. Any effort to increase the total magnification beyond this figure will yield no additional detail and is referred to as empty magnification.

Although a new student of the microscope may be tempted to immediately choose the high- est magnifying power available to view a specimen, the experienced microscopist weighs a num- ber of important factors before choosing a magnifying power. A first consideration must be the size of the specimen area, or the field of view, that the examiner wishes to study. As magnifying power increases, the field of view decreases. Thus, it is best to first select a low magnification in which a good general overall view of the specimen is seen and to switch later to a higher power in which a smaller portion of the specimen can be viewed in more detail.

The depth of focus is also a function of magnifying power. After a focus has been achieved on a specimen, the depth of focus defines the thickness of that specimen. Areas above and below this region will be blurred and can be viewed only when the focus is readjusted. Depth of focus decreases as magnifying power increases.

The Comparison Microscope Forensic microscopy often requires a side-by-side comparison of specimens. This kind of examination can best be performed with a comparison microscope, such as the one pictured in Figure 7–5. Basi- cally, the comparison microscope is two compound microscopes combined into one unit. The unique feature of its design is that it uses a bridge incorporating a series of mirrors and lenses to join two independent objective lenses into a single binocular unit. When a viewer looks through the eyepiece lenses of the comparison microscope, a circular field, equally divided into two parts by a fine line, is observed. The specimen mounted under the left-hand objective is seen in the left half of the field, and the specimen under the right-hand objective is observed in the right half of the field. It is important to closely match the optical characteristics of the objective lenses to ensure that both specimens are seen at equal magnification and with minimal but identical lens distortions. Comparison microscopes de- signed to compare bullets, cartridges, and other opaque objects are equipped with vertical or reflected illumination. Comparison microscopes used to compare hairs or fibers use transmitted illumination.

Figure 7–6 shows the striation markings on two bullets that have been placed under the objective lenses of a comparison microscope. Modern firearms examination began with the

condenser The lens system under the micro- scope stage that focuses light onto the specimen

parfocal Describes a microscope such that when an image is focused with one objective in position, the other objective can be rotated into place and the field will remain in focus.

monocular Describes a microscope with one eyepiece.

binocular Describes a microscope with two eyepieces.

depth of focus The thickness of a specimen that is entirely in focus under a microscope.

WEBEXTRA 7.1 Explore the Concept of Magnifica- tion with a Compound Microscope

WEBEXTRA 7.2 Scan a Sample under the Compound Microscope

WEBEXTRA 7.3 Observe the Concept of Depth of Focus

field of view The area of the specimen that can be seen after it is magnified.

WEBEXTRA 7.4 Practice Matching Bullets with the Aid of a 3-D Interactive Illustration

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FIGURE 7–5 The comparison microscope—two independent objective lenses joined together by an optical bridge.

FIGURE 7–6 Photomicrograph taken through a comparison microscope. On the right are the striation markings on the test-fired bullet, fired through the sus- pect weapon. On the left are the markings of the crime-scene bullet.

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introduction of the comparison microscope, with its ability to give the firearms examiner a side- by-side magnified view of bullets. Bullets that are fired through the same rifle barrel display comparable rifling markings on their surfaces. Matching the majority of striations present on each bullet justifies a conclusion that both bullets traveled through the same barrel.

The Stereoscopic Microscope The details that characterize the structures of many types of physical evidence do not always require examination under very high magnifications. For such specimens, the stereoscopic microscope has proven quite adequate, providing magnifying powers from 103 to 1253. This microscope has the advantage of presenting a distinctive three-dimensional image of an object. Also, whereas the image formed by the compound microscope is inverted and reversed (upside- down and backward), the stereoscopic microscope is more convenient because of the prisms in its light path that permit the formation of a right-side-up image. The stereoscopic microscope, shown in Figure 7–7, is actually two monocular compound microscopes properly spaced and aligned to present a three-dimensional image of a specimen to the viewer, who looks through both eyepiece lenses. The light path of a stereoscopic microscope is shown in Figure 7–8.

The stereoscopic microscope is undoubtedly the most frequently used and versatile micro- scope found in the crime laboratory. Its wide field of view and great depth of focus make it an ideal instrument for locating trace evidence in debris, garments, weapons, or tools. Furthermore, its potentially large working distance (the distance between the objective lens and the specimen) makes it quite applicable for the microscopic examination of big, bulky items. When fitted with vertical illumination, the stereoscopic microscope becomes the primary tool for characterizing physical evidence as diverse as paint, soil, gunpowder residues, and marijuana.

FIGURE 7–7 A stereoscopic microscope.

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WEBEXTRA 7.5 Explore the Stereoscopic Microscope

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The Polarizing Microscope Light’s wavelike motion in space can be invoked to explain many facets of its behavior. The po- larizing microscope takes advantage of one of these facts—the fact that light vibrates.

Polarization The waves that compose a beam of light can be pictured as vibrating in all directions perpendicu- lar to the direction in which the light is traveling. However, when a beam of light passes through certain types of specially fabricated crystalline substances, it emerges vibrating in only one plane. Light that is confined to a single plane of vibration is said to be plane-polarized. The device that polarizes light in this manner is called a polarizer. A common example of this phenomenon is the passage of sunlight through polarized sunglasses. By transmitting light vibrating in the vertical plane only, these sunglasses eliminate or reduce light glare. Most glare consists of partially polar- ized light that has been reflected off horizontal surfaces and thus is vibrating in a horizontal plane.

Because polarized light appears no different to the eye from ordinary light, special means must be devised for detecting it. This is accomplished simply by placing a second polarizing crystal, called an analyzer, in the path of the polarized beam. As shown in Figure 7–9, if the polarizer and analyzer are aligned parallel to each other, the polarized light passes through and is seen by the eye. If, on the other hand, the polarizer and analyzer are set perpendicular to one another, or are “crossed,” no light penetrates, and the result is total darkness or extinction.

In this manner, a compound or stereoscopic microscope can be outfitted with a polarizer and analyzer to allow the viewer to detect polarized light. Such a microscope is known as a polarizing microscope. Essentially, the polarizer is placed between the light source and the sample stage to polarize the light before it passes through the specimen. The polarized light penetrating the

FIGURE 7–8 Schematic diagram of a stereo- scopic microscope. This microscope is actually two separate monocular microscopes, each with its own set of lenses except for the lowest objective lens, which is common to both microscopes.

plane-polarized light Light confined to a single plane of vibration.

polarizer A device that permits the passage of light waves vibrating in only one plane.

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specimen must then pass through an analyzer before it reaches the eyepiece and finally the eye. Normally, the polarizer and analyzer are “crossed” so that when no specimen is in place, the field appears dark. However, introducing a specimen that polarizes light reorients the polarized light, allowing it to pass through the analyzer. This result produces vivid colors and intensity contrasts that make the specimen readily distinguishable.

Applications of the Polarized Microscope The most obvious and important applications of this microscope relate to studying materials that polarize light. For example, as we will learn in Chapter 9 (see page 214), many crystalline sub- stances are birefringent; that is, they split a beam of light into two light-ray components of differ- ent refractive index values. What makes this observation particularly relevant to our discussion of the polarizing microscope is that the light beams are polarized at right angles to each other. Thus, polarizing microscopy has found wide application for the examination of birefringent minerals present in soil. By using the immersion method and selecting the proper immersion liquids, a refractive index corresponding to each plane of polarized light can be determined. Thus, when a mineral is viewed under polarized light in a liquid that matches one of its refractive indices, the Becke line will no longer be visible. This information, plus observations on crystal color, form, and so on, makes it possible for the microscopist to identify the mineral. Similarly, criminalists use the fact that many synthetic fibers are birefringent to characterize them with a polarizing microscope.

The Microspectrophotometer From a practical point of view, few instruments in a crime laboratory can match the versatility of the microscope. The microscope’s magnifying power is indispensable for finding minute traces of physical evidence. Many items of physical evidence can be characterized by a microscopic examination of their morphological features. Likewise, the microscope can be used to study how light interacts with the material under investigation, or it can be used to observe the effects that other chemical substances have on such evidence. Each of these features allows an examiner to better characterize and identify physical evidence. Recently, linking the microscope to a com- puterized spectrophotometer has added a new dimension to its capability. This combination has given rise to a new instrument called the microspectrophotometer.

In many respects, this is an ideal marriage from the forensic scientist’s viewpoint. In Chapter 11, we will see how a chemist can use selective absorption of light by materials to characterize them. In particular, light in the ultraviolet, visible, and infrared regions of the electromagnetic spec- trum is most helpful for this purpose. Unfortunately, in the past, forensic chemists were unable to take full advantage of the capabilities of spectrophotometry for examining trace evidence because most spectrophotometers are not well suited for examining the very small particles frequently

Light source

Polarizer

Analyzer transmits polarized light

Analyzer turned through 90˚ does not transmit polarized light

No light

Polarized light

Polarized light containing only vertical vibrations

Light containing all vibrations

FIGURE 7–9 Polarization of light.

WEBEXTRA 7.6 Explore the Polarizing Microscope—I

WEBEXTRA 7.7 Explore the Polarizing Microscope—II

microspectrophotometer An instrument that links a micro- scope to a spectrophotometer.

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encountered as evidence. However, with the development of the microspectrophotometer, a fo- rensic analyst can now view a particle under a microscope while a beam of light is directed at the particle in order to obtain its absorption spectrum. Depending on the type of light employed, an examiner can acquire either a visible or an infrared (IR) spectral pattern of the substance being viewed under the microscope. The obvious advantage of this approach is to provide the forensic scientist with added information that will characterize trace quantities of evidence. A microspec- trophotometer designed to measure the uptake of visible light by materials is shown in Figure 7–10.

Visual comparison of color is usually one of the first steps in examining paint, fiber, and ink evidence. Such comparisons are easily obtained using a comparison microscope. Now, with the use of the microspectrophotometer, not only can the color of materials be compared visually but, at the same time, an absorption spectrum can be plotted for each item under examination to display the exact wavelengths at which it absorbs in the visible-light spectrum. Occasionally colors that appear similar by visual examination show significant differences in their absorption spectra. An example of this approach is shown in Figure 7–11, in which the microspectrophotometer is used to distinguish counterfeit and authentic currency by comparing the spectral patterns of inked lines on currency.

Another emerging technique in forensic science is the use of the infrared microspectro- photometer to examine fibers and paints. The “fingerprint” IR spectrum (see discussion in Chapter 11) is unique for each chemical substance. Therefore, obtaining such a spectrum from either a fiber or a paint chip allows the analyst to better identify and compare the type of chemi- cals from which these materials are manufactured. With a microspectrophotometer, a forensic analyst can view a substance through the microscope and at the same time have the instrument plot the infrared absorption spectrum for that material.

The Scanning Electron Microscope (SEM) All the microscopes described thus far use light coming off the specimen to produce a magnified image. The scanning electron microscope is, however, a special case in the family of microscopes (see Figure 7–12). The image is formed by aiming a beam of electrons onto the specimen and

FIGURE 7–10 A visible-light microspectrophotometer.

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studying electron emissions on a closed TV circuit. The beam of electrons is emitted from a hot tungsten filament and is focused by electromagnets onto the surface of the specimen. This pri- mary electron beam causes the emission of electrons, known as secondary electrons, from the elements that make up the upper layers of the specimen. Also, 20–30 percent of the primary electrons rebound off the surface. These electrons are known as backscattered electrons. The emitted electrons (both secondary and backscattered) are collected and the amplified signal is displayed on a monitor. By scanning the primary electron beam across the specimen’s surface in

% Reflectance 50

400 500 600 700 Wavelength (nm)

% Reflectance 50

400 500 600 700 Wavelength (nm)

FIGURE 7–11 Two $50 bills are shown at top; one is genuine and the other is counterfeit. Below each bill is a microphotograph of an inked line present on each bill. Each line was examined under a visible-light microspectrophotometer. As shown, the visible absorption spectrum of each line is readily differentiated, thus allowing the examiner to distinguish a counter- feit bill from genuine currency.

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synchronization with the cathode-ray tube, it is possible to convert the emitted electrons into an image of the specimen for display on the cathode-ray tube.

The major attractions of the SEM image are its high magnification, high resolution, and great depth of focus. In its usual mode, the SEM has a magnification that ranges from 103 to 100,0003. Its depth of focus is some 300 times better than optical systems at similar magnifica- tions, and the resultant picture is almost stereoscopic in appearance. Its great depth of field and magnification are exemplified by the magnification of cystolithic hair on the marijuana leaf, as shown in Figure 7–13. An SEM image of a vehicle’s headlight filaments may reveal whether the headlights were on or off at the time of a collision (see Figures 7–14 and 7–15).

Another facet of scanning electron microscopy has been the use of X-ray production to deter- mine the elemental composition of a specimen. X-rays are generated when the electron beam of the scanning electron microscope strikes a target. When the SEM is coupled to an X-ray analyzer, the emitted X-rays can be sorted according to their energy values and used to build up a picture of the elemental distribution in the specimen. Because each element emits X-rays of characteristic energy values, the X-ray analyzer can identify the elements present in a specimen. Furthermore, the element’s concentration can be determined by measuring the intensity of the X-ray emission.

Forensic Palynology: Pollen and Spores as Evidence Of the many plant species on earth, more than half a million produce pollen or spores. The pollen or spores produced by each species has a unique type of ornamentation and mor- phology. This means that pollen or spores can be identified and used to link a crime scene

FIGURE 7–12 A scanning electron microscope.

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WEBEXTRA 7.8 Explore the Scanning Electron Microscope

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FIGURE 7–13 The cystolithic hairs of the marijuana leaf, as viewed with a scanning electron microscope (8003).

FIGURE 7–14 The melted ends of a hot filament break indicate that the headlights were on when an accident occurred.

FIGURE 7–15 The sharp ends of a cold filament break indicate that the headlights were off when an accident occurred.

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and a person or object if examined by a trained analyst. This technique is called forensic palynology and includes the collection and examination of pollen and spores connected with crime scenes, illegal activities, or terrorism. Microscopy is the principal tool used in the field of forensic palynology.

Characteristics of Spores and Pollen In nature, pollen grains are the single-celled male gametophytes (reproductive cells) of seed- bearing plants. The pollen grain wall (exine) is durable because it protects and carries the “sperms” needed for plant reproduction. Spores consist of both the male and female gametes of plants such as algae, fungi, mosses, and ferns. Pollen-producing plants are either anemophilous (their pollen is dispersed by wind) or entomophilous (their pollen is carried and dispersed by insects or small animals). Fairly precise geographical locations can often be identified by the presence of different mixtures of air- borne pollens produced by anemophilous plants. For example, it may be possible to identify a geographical origin using a profile of the pollen samples retrieved from a suspect’s clothing by ana- lyzing the type and percentages of airborne pollen grains. Entomophilous plants usually produce a

Detecting Gunshot Residue

One application of scanning electron microscopy has been to determine whether a suspect has recently fired a gun. In this case, an attempt is made to remove any gunshot particles that remain on a shooter’s hands by lifting them off with a piece of adhesive tape. The tape is then examined under the SEM for the presence of particles that may have originated from the bullet primer. These particles can be characterized by their

inside the science size, shape, and elemental composition. As shown in the figure, when the sample of gunshot residue is exposed to a beam of electrons from the scanning electron microscope, X-rays are emitted. These X-rays are passed into a detector, where they are converted into electrical signals. These signals are sorted and displayed according to the energies of the emitted X-rays. Through the use of this technique, the elements lead, antimony, and barium, frequently found in most primers, can be rapidly detected and identified.

ELECTRON GUN

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DISPLAY

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A schematic diagram of a scanning electron microscope displaying the image of a gunshot residue particle. Simultaneously, an X-ray analyzer detects and displays X-ray emissions from the elements lead (Pb), antimony (Sb), and barium (Ba) present in the particle.

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small amount of pollen that is very sticky in nature. Therefore, this type of pollen is rarely deposited on clothing or other objects except by direct contact with the plant. This information is useful when reconstructing the events of a crime because it may indicate that the clothing, a vehicle, or other ob- jects on which this pollen is found came into direct contact with plant types found at a crime scene.

Analysis of Spores and Pollen Both spores and pollen are microscopic in size and are produced by adult plants and then dispersed by the millions, and both can be analyzed using similar methods that use a variety of microscopic techniques. Using a compound light microscope with magnification capabilities up to 1,0003, analysts usually can identify pollen and spores as having come from a specific plant family or genus, and sometime even the unique species. However, often the pollen or spores of related species may look so similar that identification of the species is possible only by careful analysis using a scanning electron microscope (SEM) (see Figure 7–16).

Unique shapes, aperture type, and surface ornamentation are typically used to identify spore samples. Useful features for characterizing pollen grains include shape, apertures, and wall and surface sculpturing. Shapes of pollen grains include spheres, triangles, ellipses, hexagons, pentagons, and many other geometric variations. Aper- tures are the openings on pollen grains from which the pollen tube grows and carries the sperms to the egg to complete fertilization. Sculpturing of the pollen refers to the pattern of the pollen grain surface.

To avoid destruction or contamination of pollen evidence, early collection of forensic pollen samples for analysis is important and should be completed as soon as possible at a crime scene by a trained palynologist. This expert’s first task is to calculate the estimated production and dispersal patterns of spores and pollen (called the pollen rain) for the crime scene or area of interest and, using that information, to produce a kind of “pollen finger- print” of that location.

The information gained from the analysis of pollen and spore evidence has many possible uses. It can link a suspect or object to the crime scene or the victim, prove or disprove a suspect’s alibi, include or exclude suspects, track the previous whereabouts of some item or suspect, or indicate the geographical origin of some item. In the past, pollen and spore evidence has been used to locate human remains and concealed burial sites, establish the season or time of death of a victim, locate the source areas of illegal drugs and fake pharmaceuticals, identify terrorists, and prove the perpetration of illegal poaching and the adulteration of commercial foods.

FIGURE 7–16 Scanning electron micrograph of ragweed pollen at a magnification of 11703 if the image is printed 10 cm wide.

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Clues from the Cornfield A case exemplifying the application of forensic palynology to a criminal investigation occurred when a victim was kidnapped, robbed, and then murdered in the eastern part of the Ameri- can Midwest. The victim’s car was stolen but later abandoned when it got stuck in mud near a busy highway. The next night a drifter was arrested in a nearby town for breaking into a closed store. While in jail awaiting trial, the drifter told a fellow in- mate about his car being stuck in the mud and that he would not be in jail but for that mishap. The other prisoner, hoping to work a deal for a lighter sentence, told this story to the sheriff.

During the investigation of the crime scene, one of the law enforcement agents noticed that there was a large field of mature corn (maize, Zea mays) growing between the dirt road where the stolen car had been abandoned in the mud and the nearby highway leading to the next town. The investigator wondered if traces of torn maize leaves on the suspect’s cloth- ing might link him to the crime scene. Fortunately, the drifter’s shirt and pants had been removed and stored in sterile paper

bags when he was arrested. As with all prisoners in that region, he had been given a pair of orange overalls to wear while in jail.

The shirt and pants were sent to a botanist who was asked to search for traces of maize leaves on the clothing. The bota- nist was also a palynologist and thus also collected samples and searched for traces of pollen. The pollen samples provided the best results. The samples collected from the suspect’s shirt revealed that the neck and shoulder region of the shirt had high concentrations of fresh maize pollen. The forensic sample col- lected from the pants also contained maize pollen, but in a lower percentage. The forensic pollen data indicated that the drifter had recently walked through a maize field similar to the one between the abandoned car and the highway. As he walked through the field, he had brushed against blooming male tassels on the corn plants that were about head high. This accounted for the high amount of maize pollen found on the shoulder and neck area of the shirt. Lesser amounts of maize pollen also fell on his pants as he walked through the field. While the suspect awaited trial, additional evidence and several fingerprints from the victim’s farm also linked him to the murder.

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A microscope is an optical instrument that uses a lens or a combination of lenses to magnify and resolve the fine de- tails of an object. Various types of microscopes are used to analyze forensic specimens. In the basic compound micro- scope, the object to be magnified is placed under the lower lens, called the objective lens, and the magnified image is viewed through the upper lens, known as the eyepiece lens. Forensic microscopy often requires side-by-side compari- son of specimens. The comparison microscope consists of two independent objective lenses joined together by an opti- cal bridge to a common eyepiece lens. When a viewer looks through the eyepiece lens of the comparison microscope, the objects under investigation are observed side-by-side in a circular field that is equally divided into two parts. Mod- ern firearms examination began with the introduction of the comparison microscope, with its ability to give the firearms examiner a side-by-side magnified view of bullets. The ste- reoscopic microscope is actually two monocular compound microscopes properly spaced and aligned to present a three- dimensional image of a specimen to the viewer, who looks through both eyepiece lenses. Its large working distance makes it quite applicable for the microscopic examination of big, bulky items.

Light that is confined to a single plane of vibration is said to be plane-polarized. The examination of the interaction of plane-polarized light with matter is made possible with the polarizing microscope. Polarizing microscopy has found wide applications for the study of birefringent materials, that is, materials that have a double refraction. These refractive in- dex data help identify minerals present in a soil sample or the identity of a manufactured fiber. The microspectrophotometer is a spectrophotometer coupled with a light microscope. The examiner studying a specimen under a microscope can simul- taneously obtain the visible absorption spectrum or IR spec- trum of the material being observed.

Finally, the scanning electron microscope (SEM) bom- bards a specimen with a beam of electrons instead of light to produce a highly magnified image from 103 to 100,0003. The bombardment of the specimen’s surface with electrons normally produces X-ray emissions that can be used to char- acterize elements present in the material under investigation.

Forensic palynology involves the collection and examina- tion of pollen and spores connected with crime scenes, illegal activities, or terrorism. The microscope is the principal tool used in the field of forensic palynology.

chapter summary

review questions

11. A microscope that remains in focus regardless of which objective lens is rotated into place is ___________.

12. A microscope with only one eyepiece is ___________; one with two eyepieces is ___________.

13. Each microscope lens is inscribed with a number signi- fying its ___________.

14. An eyepiece lens of 103 used in combination with an objective lens of 203 has a total magnification power of ___________.

15. The ability of an objective lens to resolve details into sep- arate images is directly proportional to its ___________.

16. The size of the specimen area in view is known as the ___________.

17. As magnification increases, the field of view (increases, decreases).

18. The thickness of a specimen in view is known as the ___________.

19. The depth of focus (increases, decreases) with increas- ing magnification.

20. A side-by-side view of two specimens is best obtained with the ___________ microscope.

1. A microscope uses a combination of ___________ to magnify an image.

2. A type of image that cannot be viewed directly is called a(n) ___________ image.

3. A(n) ___________ microscope consists of two lenses mounted at each end of a hollow tube.

4. The lens closest to the specimen is called the ___________.

5. The lens nearest the viewer’s eye is called the ___________.

6. The image seen through a compound microscope is (vir- tual, real).

7. True or False: The coarse and fine adjustments are part of the microscope’s mechanical system. ___________

8. A transparent specimen is viewed through a microscope using ___________ light.

9. An opaque object requires ___________ illumination for viewing with a microscope.

10. A(n) ___________ collects light rays from the base il- luminator and concentrates them on the specimen.

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21. True or False: A bridge is used to join two independent

objective lenses into a single binocular unit to form a comparison microscope. ___________

22. Two monocular compound microscopes properly spaced and aligned describe the ___________ microscope.

23. True or False: The stereoscopic microscope is the least frequently used microscope in a typical crime labora- tory. ___________

24. The stereoscopic microscope offers a large ___________ between the objective lens and the specimen.

25. Light confined to a single plane of vibration is said to be ___________.

26. If a polarizer and analyzer are placed (perpendicular, parallel) to each other, no light penetrates.

27. The ___________ microscope allows a viewer to detect polarized light.

28. Crystals that are ___________ produce two planes of polarized light, each perpendicular to the other.

29. By using the ___________, one can view a particle un- der a microscope while a beam of light is directed at the particle in order to obtain its absorption spectrum.

30. The ___________ microscope focuses a beam of elec- trons on a specimen to produce an image.

31. When a beam of electrons strikes a specimen, ___________ are emitted whose energies correspond to elements present in the specimen.

32. True or False: Both spores and pollen can be identi- fied and used to link a crime scene to an individual. ___________

33. True or False: Spores can be characterized by shape and surface characteristics through a simple visual exami- nation. ___________

application and critical thinking

further references

1. A forensic biologist must examine the outside of a small leaf and a thin slice of the leaf one cell thick. She has at her disposal a transmitted light microscope and a stereomicroscope (vertical illumination). What instru- ment should she use for the analysis of each object and why?

2. A trace evidence analyst places crystals of an unidenti- fied white powder onto the stage of a polarizing micro- scope and observes the crystals through the eyepiece. Under correct focus, some of the crystals show bright colors while others appear very dark and hardly distin- guishable. What can be concluded about the contents of the white powder?

3. Numerous red-colored fibers from a sexual assault crime scene are delivered to the crime lab along with red fibers from the suspect’s clothing. What instrument should the trace analyst use to view the fibers and ob- tain chemical information that could be used to com- pare the crime-scene and clothing samples?

4. Upon arriving at the crime scene of an attempted ho- micide, police officers observe a man fleeing the scene and apprehend him. He is suspected to be the shooter in the attempted homicide, and the police wish to test his hands for the presence of compounds consistent with gunshot residue. How should they proceed?

Bartick, E. G., “Infrared Microscopy and Its Forensic Ap- plications,” in R. Saferstein, ed., Forensic Science Hand- book, vol. 3, 2nd ed. Upper Saddle River, N.J.: Prentice Hall, 2010.

“Basic Concepts in Optical Microscopy,” http://micro .magnet.fsu.edu/primer/anatomy/anatomy.html

De Forest, Peter R., “Foundations of Forensic Microscopy,” in R. Saferstein, ed., Forensic Science Handbook, vol. 1, 2nd ed. Upper Saddle River, N.J.: Prentice Hall, 2002.

Eyring, Michael B., “Visible Microscopical Spectropho- tometry in the Forensic Sciences,” in R. Saferstein, ed.,

Forensic Science Handbook, vol. 1, 2nd ed. Upper Saddle River, N.J.: Prentice Hall, 2002.

Palenik, S., and C. Palenik, “Microscopy and Microchemis- try of Physical Evidence,” in R. Saferstein, ed., Forensic Science Handbook, vol. 2, 2nd ed. Upper Saddle River, N.J.: Prentice Hall, 2005.

Petraco, N., and T. Kubic, Basic Concepts in Optical Microscopy for Criminalists, Chemists, and Conservators. Boca Raton, Fla.: CRC Press, 2004.

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The Beltway Snipers

During a three-week period in October 2002, ten people were killed and three others were wounded as two snipers terrorized the region in and around the Baltimore–Washington metropolitan area. The arrest of John Allen Muhammad, 41, and Lee Boyd Malvo, 17, ended the ordeal. The semiautomatic .223-caliber rifle seized from them was ultimately linked by ballistics tests to eight of the ten killings. The car that Muhammad and Malvo were driving had been specially configured with one hole in the trunk through which a rifle barrel could protrude, so that a sniper could shoot from inside a slightly

ajar trunk. The major break in the case came when a friend of Muhammad’s

called police suggesting that Muhammad and his friend Malvo were the likely snipers. Muhammad’s automobile records revealed numerous traffic stops in the Beltway area during the

time of the shootings. Another break in the case came when Malvo called a priest to boast of a killing weeks before in Montgomery, Alabama. Investigators traced the claim to a recent liquor store holdup that left one person dead. Fortunately, the perpetrator of this crime left a latent fingerprint at the murder scene. Authorities quickly tracked the print to Malvo, a Jamaican citizen, through his fingerprints on file with the Immigration and Naturalization Service. A description of Muhammad’s car was released to the media, leading to tips from alert citizens who noticed the car parked in a rest area with both occupants asleep.

The motive for the shooting spree was believed to be a planned plot to extort $10 million from local and state governments. Muhammad was recently executed, and Malvo is currently serving life imprisonment without parole.

headline news

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After studying this chapter you should be able to:

firearms, tool marks, and other impressions

bore breechface caliber choke distance determination ejector extractor firearms identification gauge Greiss test grooves lands rifling

KEY TERMS

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168 CHAPTER 8

Just as natural variations in skin ridge patterns and characteristics provide a key to human iden- tification, minute random markings on surfaces can impart individuality to inanimate objects. Structural variations and irregularities caused by scratches, nicks, breaks, and wear permit the criminalist to relate a bullet to a gun; a scratch or abrasion mark to a single tool; or a tire track to a particular automobile. Individualization, so vigorously pursued in all other areas of criminalis- tics, is frequently attainable in firearms and tool mark examination.

Although a portion of this chapter will be devoted to the comparison of surface features for the purposes of bullet identification, a complete description of the services and capabilities of the modern forensic firearms laboratory cannot be restricted to just this one subject, important as it may be. The high frequency of shooting cases means that the science of firearms identification must extend beyond mere comparison of bullets to include knowledge of the operation of all types of weapons, restoration of obliterated serial numbers on weapons, detection and characterization of gunpowder residues on garments and around wounds, estimation of muzzle-to-target distances, and detection of powder residues on hands. Each of these functions will be covered in this chapter.

Types of Firearms Generally, firearms can be divided into two categories: handguns and long guns. Handguns, or pistols, are firearms that are designed to be held and fired with one hand. The three most common types of handguns are single-shot handguns, revolvers, and semiautomatics. All handguns can be classified as single-action or double-action firearms. Single-action firearms require the hammer to be manually cocked backward each time before the trigger is pulled in order to fire. Double- action firearms cock the hammer when the trigger is pulled and then reload the firing chamber after the round is fired.

Single-shot pistols can fire only one round, or shot, at a time. Each round must be manually loaded into the chamber before firing.

The revolver features several firing chambers located within a revolving cylinder. As the revolver is fired, the cylinder can rotate clockwise or counterclockwise. Each firing chamber holds one cartridge, which is lined up with the barrel mechanically when the round is fired. The cartridge cases have to be manually ejected to reload the firing chambers. Swing-out revolvers feature a cylinder that swings out to the side of the weapon to be loaded (see Figure 8–1). Break-top revolvers are hinged so that both the barrel and the cylinder flip downward for loading.

firearms identification A discipline mainly concerned with determining whether a bullet or cartridge was fired by a particular weapon; it is not to be confused with ballistics, which is the study of a projectile in motion.

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FIGURE 8–1 A swing-out revolver features a cylinder that swings out to the side of the weapon to be loaded.

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FIREARMS, TOOL MARKS, AND OTHER IMPRESSIONS 169

Solid-frame revolvers have no mechanism to uncover all the firing chambers at once. Instead, a small “gate” at the back of the gun allows one chamber to be loaded at a time; the cylinder is then rotated, and the next chamber is loaded with a cartridge.

Semiautomatic pistols feature a removable magazine that is most often contained within the grip of the firearm. Once the magazine is loaded, the hammer is cocked by pulling the slide on the top of the gun rearward and then releasing it to load the first round. The firing of the car- tridge generates gases that are used to eject the cartridge case, cock the hammer, and load the next round. A semiautomatic pistol (see Figure 8–2) fires one shot per trigger pull. An automatic firearm, such as a machine gun, fires as long as the trigger is pressed or until the ammunition is depleted.

Long guns are either rifles or shotguns. Rifles and shotguns are designed to be fired while resting on the shoulder. The two principal differences between rifled firearms and shotguns are found in the ammunition and the barrel. Shotgun ammunition, called a shell, contains numer- ous ball-shaped projectiles, called shot. The barrel of a shotgun is smooth, without the grooves and lands found in rifles. A shotgun barrel can also be narrowed toward the muzzle in order to concentrate shot when fired. This narrowing of the barrel is called the choke of the shotgun. A shotgun may be single or double barreled. The two barrels of a double-barreled shotgun may be arranged horizontally (side by side) or vertically (one over another). The barrels may also have different choke diameters.

The various types of rifles and shotguns have different reloading mechanisms. The single-shot gun can chamber and fire only one round at a time. Just as with single-shot pistols, the round has to be loaded manually each time. Repeating long guns use a mechanical instrument of some sort to eject spent cartridges, load a new round, and cock the hammer after a round is fired. These include lever-action, pump or slide-action, bolt-action (see Figure 8–3), and semiautomatic (see Figure 8–4) long guns, the names of which refer to the loading mechanism used on each. Semiautomatic rifles use the force of the gas produced during firing to eject the spent cartridge, load a new round, and cock the hammer. Semiauto- matic firearms use a disconnector mechanism to fire one shot per trigger pull, whereas fully automatic firearms do not have such a mechanism and fire multiple consecutive shots with a single pull of the trigger.

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FIGURE 8–2 A semiautomatic pistol.

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170 CHAPTER 8

Bullet and Cartridge Comparisons The inner surface of the barrel of a gun leaves its markings on a bullet passing through it. These markings are peculiar to each gun. Hence, if one bullet found at the scene of a crime and another test-fired from a suspect’s gun show the same markings, the suspect is linked to the crime. Be- cause these inner surface striations are so important for bullet comparison, it is important to know why and how they originate.

The Gun Barrel The gun barrel is produced from a solid bar of steel that has been hollowed out by drilling. The microscopic drill marks left on the barrel’s inner surface are randomly irregular and in them- selves impart a uniqueness to each barrel. However, the manufacture of a barrel requires the additional step of impressing its inner surface with spiral grooves, a step known as rifling. The surfaces of the original bore remaining between the grooves are called lands (see Figure 8–5). As a fired bullet travels through a barrel, it engages the rifling grooves; these grooves then guide the bullet through the barrel, giving it a rapid spin. This is done because a spinning bullet does not tumble end over end on leaving the barrel, but remains instead on a true and accurate course.

The diameter of the gun barrel, sketched in Figure 8–6, measured between opposite lands, is known as the caliber of the weapon. Caliber is normally recorded in hundredths of an inch or in millimeters—for example, .22 caliber and 9 mm. Actually, the term caliber, as it is commonly

FIGURE 8–3 A bolt-action long gun uses the movement of a bolt mechanism to expel the spent cartridge case, load the next round, and cock the hammer.

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FIGURE 8–4 A semiautomatic long gun uses the energy from the firing reaction to expel the spent cartridge case, load the next round, and cock the hammer.

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grooves The cut or low-lying portions be- tween the lands in a rifled bore.

rifling The spiral grooves formed in the bore of a firearm barrel that impart spin to the projectile when it is fired.

bore The interior of a firearm barrel.

lands The raised portion between the grooves in a rifled bore.

caliber The diameter of the bore of a rifled firearm; the caliber is usually expressed in hundredths of an inch or millimeters—for example, .22 caliber and 9 mm.

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applied, is not an exact measurement of the barrel’s diameter; for example, a .38-caliber weapon may actually have a bore diameter that ranges from 0.345 to 0.365 inch.

RIFLING METHODS Before 1940, barrels were rifled by having one or two grooves at a time cut into the surface with steel hook cutters. The cutting tool was rotated as it passed down the barrel, so that the final results were grooves spiraling either to the right or left. However, as the need for increased speed in the manufacture of weapons became apparent, newer techniques were developed that were far more suitable for the mass production of weapons.

The broach cutter consists of a series of concentric steel rings, with each ring slightly larger than the preceding one. As the broach passes through the barrel, it simultaneously cuts all grooves into the barrel at the required depth. The broach rotates as it passes through the barrel, giving the grooves their desired direction and rate of twist. A single broach cutter ring is shown in Figure 8–7.

In contrast to the broach, the button process involves no cuttings. A steel plug or “button” impressed with the desired number of grooves is forced under extremely high pressures through the barrel. A single pass of the button down the barrel compresses the metal to create lands and grooves on the barrel walls that are negative forms of those on the button. The button rotates to produce the desired direction and rate of twist (see Figure 8–8).

FIGURE 8–5 Interior view of a gun barrel, showing the presence of lands and grooves.

FIGURE 8–6 Cross section of a barrel with six grooves. The diameter of the bore is the caliber.

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FIGURE 8–7 A segment of a broach cutter.

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172 CHAPTER 8

Like the button process, the mandrel rifling or hummer forging process involves no cutting of metal. A mandrel is a rod of hardened steel machined so its form is the reverse impression of the rifling it is intended to produce. The mandrel is inserted into a slightly oversized bore, and the barrel is compressed with hammering or heavy rollers into the mandrel’s form.

Every firearms manufacturer chooses a rifling process that is best suited to meet the produc- tion standards and requirements of its product. Once the choice is made, however, the class char- acteristics of the weapon’s barrel will remain consistent; each will have the same number of lands and grooves, with the same approximate width and direction of twist. For example, .32-caliber Smith & Wesson revolvers have five lands and grooves twisting to the right. On the other hand, Colt .32-caliber revolvers exhibit six lands and grooves twisting to the left. Although these class characteristics permit the examiner to distinguish one type or brand name of weapon from an- other, they do not impart individuality to any one barrel; no class characteristic can do this.

If one could cut a barrel open lengthwise, a careful examination of the interior would re- veal the existence of fine lines, or striations, many running the length of the barrel’s lands and grooves. These striations are impressed into the metal as the negatives of minute imperfections found on the rifling cutter’s surface, or they are produced by minute chips of steel pushed against the barrel’s inner surface by a moving broach cutter. The random distribution and irregularities of these markings are impossible to duplicate exactly in any two barrels. No two rifled barrels, even those manufactured in succession, have identical striation markings. These striations form the individual characteristics of the barrel.

COMPARING BULLET MARKINGS As the bullet passes through the barrel, its surface is impressed with the rifled markings of the barrel. The bullet emerges from the barrel carrying the impressions of the bore’s interior surface; these impressions reflect both the class and individual characteristics of the barrel (see Figure 8–9). Because there is no practical way of making a direct comparison between the markings on the fired bullet and those found within a barrel, the examiner must obtain test bullets fired through the suspect barrel for comparison. To prevent damage to the test bullet’s markings and to facilitate the bullet’s recovery, test firings are normally made into a recovery box filled with cotton or into a water tank.

The number of lands and grooves, and their direction of twist, are obvious points of com- parison during the initial stages of the examination. Any differences in these class characteristics immediately eliminate the possibility that both bullets traveled through the same barrel. A bullet with five lands and grooves could not possibly have been fired from a weapon of like caliber with

FIGURE 8–8 (Top) Cross-section of a .22-caliber rifled barrel. (Bottom) A button used to produce the lands and grooves in the barrel.

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six lands and grooves, nor could one having a right twist have come through a barrel impressed with a left twist. If both bullets carry the same class characteristics, the analyst must begin to match the striated markings on both bullets. This can be done only with the assistance of the comparison microscope (see Chapter 7).

Modern firearms identification began with the development and use of the comparison mi- croscope. This instrument is the most important tool at the disposal of the firearms examiner. The test and evidence bullets are mounted on cylindrical adjustable holders beneath the objective lenses of the microscope, each pointing in the same direction (see Figure 8–10). Both bullets are observed simultaneously within the same field of view, and the examiner rotates one bullet until a well-defined land or groove comes into view. Once the striation markings are located, the other bullet is rotated until a matching region is found. Not only must the lands and grooves of the test and evidence bullet have identical widths, but the longitudinal striations on each must coincide. When a matching area is located, the two bullets are simultaneously rotated to obtain additional matching areas around the periphery of the bullets. Figure 8–11 shows a typical photomicrograph of a bullet match as viewed under a comparison microscope.

CONSIDERATIONS IN BULLET COMPARISON Unfortunately, the firearms examiner rarely encounters a perfect match all around the bullet’s periphery. The presence of grit and rust can alter the markings on bullets fired through the same barrel. More commonly, recovered evidence bullets may become so mutilated and distorted on impact as to yield only a small area with intact markings.

Furthermore, striation markings on a barrel are not permanent structures; they are subject to continuing change and alteration through wear as succeeding bullets traverse the length of the barrel. Fortunately, in most cases, these changes are not dramatic and do not prevent the matching of two bullets fired by the same weapon. As with fingerprint comparison, there

FIGURE 8–9 A bullet is impressed with the rifling markings of the barrel when it emerges from the weapon.

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FIGURE 8–10 A bullet holder beneath the objective lens of a compari- son microscope.

FIGURE 8–11 Photomicrograph of two bullets through a compari- son microscope. The test bullet is on the right; the questioned bullet is on the left.

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FIREARMS, TOOL MARKS, AND OTHER IMPRESSIONS 175

are no hard-and-fast rules governing the minimum number of points required for a bullet comparison. The final opinion must be based on the judgment, experience, and knowledge of the expert.

Frequently, the firearms examiner receives a spent bullet without an accompanying suspect weapon and is asked to determine the caliber and possible make of the weapon. If a bullet ap- pears not to have lost its metal, its weight may be one factor in determining its caliber. In some instances, the number of lands and grooves, the direction of twist, and the widths of lands and grooves are useful class characteristics for eliminating certain makes of weapons from consid- eration. For example, a bullet that has five lands and grooves and twists to the right could not come from a weapon manufactured by Colt because Colts are not manufactured with these class characteristics.

Sometimes a bullet has rifling marks that set it apart from most other manufactured weapons, as in the case of Marlin rifles. These weapons are rifled by a technique known as microgrooving and may have 8 to 24 grooves impressed into their barrels; few other weapons are manufactured in this fashion. In this respect, the FBI maintains a record known as the General Rifling Characteristics File. This file contains listings of class characteristics, such as land and groove width dimensions, for known weapons. It is periodically updated and distributed to the law enforcement community to help identify rifled weapons from retrieved bullets.

As previously discussed, unlike rifled firearms, a shotgun has a smooth barrel. It therefore follows that projectiles passing through a shotgun barrel are not impressed with any charac- teristic markings that can later be related back to the weapon. Shotguns generally fire small lead balls or pellets contained within a shotgun shell (see Figure 8–12). A paper or plastic wad pushes the pellets through the barrel on ignition of the cartridge’s powder charge. By weighing and measuring the diameter of the shot recovered at a crime scene, the examiner can usually determine the size of shot used in the shell. The size and shape of the recovered wad may also reveal the gauge of the shotgun used and, in some instances, may indicate the manufacturer of the fired shell.

The diameter of the shotgun barrel is expressed by the term gauge.1 The higher the gauge number, the smaller the barrel’s diameter. For example, a 12-gauge shotgun has a bore diameter of 0.730 inch as contrasted to 0.670 inch for a 16-gauge shotgun. The exception to this rule is the .410-gauge shotgun, which refers to a barrel 0.41 inch in diameter.

gauge Size designation of a shotgun, originally the number of lead balls with the same diameter as the barrel that would make a pound; for example, a 12-gauge shotgun would have a bore diameter of a lead ball 1/12 pound in weight; the only exception is the .410 shotgun, in which bore size is 0.41 inch.

1 Originally, the number of lead balls with the same diameter as the barrel would make a pound. For example, a 20-gauge shotgun has an inside diameter equal to the diameter of a lead ball that weighs 1/20 of a pound.

Priming mixture

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Primer

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Flash hole Metal head

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WEBEXTRA 8.1 Practice Matching Bullets with the Aid of a 3-D Interactive Illustration

WEBEXTRA 8.2 3-D Shotshell Illustrations

FIGURE 8–12 Cross-section of a loaded shotgun shell.

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176 CHAPTER 8

Cartridge Cases The act of pulling a trigger releases the weapon’s firing pin, causing it to strike the primer, which in turn ignites the powder. The expanding gases generated by the burning gunpowder propel the bullet forward through the barrel, simultaneously pushing the spent cartridge case or shell back with equal force against the breechface. As the bullet is marked by its passage through the barrel, the shell is also impressed with markings by its contact with the metal surfaces of the weapon’s firing and loading mechanisms. As with bullets, these markings can be reproduced in test-fired cartridges to provide distinctive points of comparison for individualizing a spent shell to a rifled weapon or shotgun.

The shape of the firing pin is impressed into the relatively soft metal of the primer on the cartridge case, revealing the minute distortions of the firing pin. These imperfections may be sufficiently random to individualize the pin impression to a single weapon. Similarly, the car- tridge case, in its rearward thrust, is impressed with the surface markings of the breechface. The breechface, like any machined surface, is populated with random striation markings that become a highly distinctive signature for individualizing its surface. Other distinctive markings that may appear on the shell as a result of metal-to-metal contact are caused by the extractor and ejector mechanism and the magazine or clip, as well as by imperfections on the fire chamber walls. Pho- tomicrographs in Figure 8–13 reveal a comparison of the firing pin and breechface impressions on evidence and test-fired shells.

Firing pin, breechface, extractor, and ejector marks may also be impressed onto the surface of the brass portion of shells fired by a shotgun. These impressions provide points for individual- izing the shell to a weapon that are just as valuable as cartridge cases discharged from a rifled firearm. Furthermore, in the absence of a suspect weapon, the size and shape of a firing pin im- pression and/or the position of ejector marks in relationship to extractor and other markings may provide some clue to the type or make of the weapon that may have fired the questioned shell, or at least may eliminate a large number of possibilities.

Automated Firearms Search Systems The use of firearms, especially semiautomatic weapons, during the commission of a crime has significantly increased throughout the United States. Because of the expense of such firearms, the likelihood that a specific weapon will be used in multiple crimes has risen. The advent of comput- erized imaging technology has made possible the storage of bullet and cartridge surface charac- teristics in a manner analogous to the storage of automated fingerprint files (see pages 133–135). Using this concept, crime laboratories can be networked, allowing them to share information on bullets and cartridges retrieved from several jurisdictions.

breechface The rear part of a firearm barrel.

extractor The mechanism in a firearm by which a cartridge of a fired case is withdrawn from the chamber.

ejector The mechanism in a firearm that throws the cartridge or fired case from the firearm.

WEBEXTRA 8.3 3-D Revolver Cartridge Illustrations

WEBEXTRA 8.4 3-D Pistol Cartridge Illustrations

WEBEXTRA 8.5 3-D Rifle Cartridge Illustrations

WEBEXTRA 8.6 View Animations to Illustrate the Firing Process and the Extraction/ Ejection Process of a Semiautomatic Pistol

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FIGURE 8–13 A comparison microscope photomicrograph showing a match between (a) firing pin impressions and (b) the breech face mark on the two shells.

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Search Systems The effort to build a national computerized database for firearms evidence in the United States had a rather confusing and inefficient start in the early 1990s. Two major federal law enforcement agencies, the FBI and the ATF, offered the law enforcement community competing and incom- patible computerized systems.

EARLY SYSTEMS The automated search system developed for the FBI was known as DRUGFIRE. This system emphasized the examination of unique markings on the cartridge casings expended by the weapon. The specimen was analyzed through a microscope attached to a video camera. The magnification allowed for a close-up view to identify individual characteristics. The image was captured by a video camera, digitized, and stored in a database. Although DRUGFIRE emphasized cartridge-case imagery, the images of highly characteristic bullet striations could also be stored in a like manner for comparisons.

The Integrated Ballistic Identification System (IBIS), developed for the Bureau of Alcohol, Tobacco, Firearms and Explosives, processed digital microscopic images of identifying features

Sacco and Vanzetti In 1920, two security guards were viciously gunned down by unidentified assailants. The security guards were transporting shoe fac- tory payroll, nearly $16,000 in cash, at the time of the robbery-murder. Eyewitnesses described the assailants as “Italian-looking,” one with a full handlebar mustache. The rob- bers had used two firearms, leaving behind three different brands of shells.

Two suspects were identified and arrested—Nicola Sacco and his friend, the amply mustachioed Bartolomeo Vanzetti. After denying owning any firearms, each was found to be in possession of a loaded pistol. In fact, Sacco’s pistol was .32-caliber, the same caliber as the crime-scene bullets. In Sacco’s pockets were found 23 bullets matching the brands of the empty shells found at the murder scene.

This case coincided with the “Red Scare,” a politically turbulent time in post–World War I America. Citizens feared socialist zealots, and the media played up these emotions. Political maneuvering and the use of the media muddied the waters surrounding the case, and the fact that both suspects belonged to anarchist political groups that advocated revolu- tionary violence against the government only incited public animosity toward them. Sympathetic socialist organizations at- tempted to turn Sacco and Vanzetti into martyrs, calling their prosecution a “witch hunt.”

The outcome of the trial ultimately depended on whether the prosecution could prove that Sacco’s pistol fired the bul- lets that killed the two security guards. At trial, the ballistics experts testified that the bullets used were no longer in produc- tion and they could not find similar ammunition to use in test

firings—aside from the unused cartridges found in Sacco’s pockets. A forensics expert for the prosecution concluded that a visual examination showed that the bullets matched, leading the jury to return a verdict of guilty. Sacco and Vanzetti were sentenced to death.

Because of continued public protests, a committee was appointed in 1927 to review the case. Around this time, Calvin Goddard, at the Bureau of Forensic Ballistics in New York, perfected the comparison microscope for use in foren- sic firearms investigations. With this instrument, two bullets are viewed side by side to compare the striations imparted to a bullet’s surface as it travels through the gun’s barrel. The committee asked Goddard to examine the bullets in question. A test-fired bullet from Sacco’s weapon was matched con- clusively by Goddard to one of the crime-scene bullets. The fates of Sacco and Vanzetti were sealed and they were put to death in 1927.

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found on both expended bullets and cartridge casings. IBIS incorporated two software programs: Bulletproof, a bullet-analyzing module, and Brasscatcher, a cartridge-case-analyzing module. A schematic diagram of Bulletproof’s operation is depicted in Figure 8–14.

NIBIN In 1999, members of the FBI and ATF joined forces to introduce the National Integrated Ballistics Information Network (NIBIN) program to the discipline of firearms examination. NIBIN guides and assists federal, state, and local laboratories interested in housing an automated search system. The new unified system incorporates both DRUGFIRE and IBIS technologies available in prior years. ATF has the overall responsibility for the system sites, whereas the FBI is responsible for the communications network.

Agencies using the new NIBIN technology produce database files from bullets and cartridge casings retrieved from crime scenes or test fires from retrieved firearms. More than two hundred law enforcement agencies worldwide have adapted to this technology. The success of the system has been proven with more than 800,000 images compiled; nationwide, law enforcement agencies have connected more than 28,000 bullets and casings to more than one crime (see Figure 8–15).

For example, in a recent case, a Houston security guard was shot and killed during a botched armed robbery. A bullet and .40-caliber Smith & Wesson cartridge casing were recovered and imaged into NIBIN. Earlier that day, a robbery-turned-double-homicide left two store clerks dead. Again, two bullets and two .40-caliber Smith & Wesson cartridge casings were recovered. Once they were processed into NIBIN, a correlation was found with the murder of the security officer and a separate aggravated robbery that occurred two weeks prior. All three crimes were linked with a firearm believed to be a .40-caliber Smith & Wesson pistol.

Processor

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FIGURE 8–14 Bulletproof configuration. The sample is mounted on the specimen manipulator and illuminated by the light source from a microscope. The image is captured by a video camera and digitized. This digital image is then stored in a database, available for retrieval and comparison. The search for a match includes analyzing the width of land and groove impressions along with both rifling and individual characteristics. The Brasscatcher software uses the same system configuration but emphasizes the analysis of expended cartridge casings rather than the expended bullets.

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Further investigation into the use of a victim’s credit card aided police in locating two sus- pects. In the possession of one suspect was a .40-caliber Smith & Wesson pistol. Once retrieved, the gun was test-fired and imaged into NIBIN. The casing from the test-fired weapon matched the evidence obtained in the robbery and the aggravated robbery-homicides. The associations were verified by traditional firearms examination comparisons performed by a firearms exam- iner. Before this computerized technology was developed, it would have taken years, or may have been impossible, to link all of these shootings to one single firearm.

In another example, the ATF laboratory in Rockville, Maryland, received 1,466 cartridge casings from the Ovcara mass burial site in Bosnia. After processing and imaging profiles for all casings, the examiners determined that 18 different firearms were used at the site. With the help of NIBIN technology and competent examiners, jurists were able to try and convict an individual for war crimes.

FIGURE 8–15 Bullets A, B, C, and D were acquired in the IBIS database at different times from dif- ferent crime scenes. D is a fragmented bullet that had only three land impressions available for acquisition. Upon the entry of bullet D, IBIS found a potential matching candidate in the database: B. On the far right, bullet D is compared to bullet B using the IBIS imaging software. Finally, a forensic firearms examiner using the actual evi- dence under a conventional comparison microscope will confirm the match between B and D.

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NIBIN serves only as a screening tool for firearms evidence. A computerized system does not replace the skills of the firearms examiner. NIBIN can screen hundreds of unsolved firearms cases and may narrow the possibilities to several firearms. However, the final comparison will be made by the forensic examiner through traditional microscopic methods.

Ballistic Fingerprinting Participating crime laboratories in the United States are building databases of bullet and car- tridge cases found at crime scenes and those fired in tests of guns seized from criminals. As these databases come online and prove their usefulness in solving crimes, law enforcement officials and the political community are scrutinizing the feasibility of scaling this concept up to create a system of ballistic fingerprinting. This system would entail the capture and storage of appropri- ate markings on bullets and cartridges test-fired from handguns and rifles before they are sold to the public. Questions regarding who will be responsible for collecting the images and details of how they will be stored are but two of many issues to be determined. The concept of ballistic fin- gerprinting is an intriguing one for the law enforcement community and promises to be explored and debated intensely in the future.

Gunpowder Residues In incidents involving gunshot wounds, it is often necessary to determine the distance from which the weapon was fired. Frequently, in incidents involving a shooting death, the individual ap- prehended and accused pleads self-defense as the motive for the attack. Such claims are fertile grounds for distance determinations because finding the proximity of the parties involved in the incident is necessary to establish the facts of the incident. Similarly, careful examination of the wounds of suicide victims usually reveals characteristics associated with a very close-range gunshot wound. The absence of such characteristics is a strong indication that the wound was not self-inflicted and signals the possibility of foul play.

Distance Determination Modern ammunition is propelled toward a target by the expanding gases created by the ignition of smokeless powder or nitrocellulose in a cartridge. Under ideal circumstances, all of the pow- der would be consumed in the process and converted into the rapidly expanding gases. However, in practice the powder is never totally burned. When a firearm is discharged, unburned and par- tially burned particles of gunpowder in addition to smoke are propelled out of the barrel along with the bullet toward the target. If the muzzle of the weapon is sufficiently close, these products are deposited onto the target. The distribution of gunpowder particles and other discharge resi- dues around the bullet hole permits an assessment of the distance from which a handgun or rifle was fired.

The accuracy of a distance determination varies according to the circumstances of the case. When the investigator is unable to recover a suspect weapon, the best that the examiner can do is to state whether a shot could have been fired within some distance interval from the target. More exact opinions are possible only when the examiner has the suspect weapon in hand and has knowledge of the type of ammunition used in the shooting.

HANDGUNS AND RIFLES The precise distance from which a handgun or rifle has been fired must be determined by careful comparison of the powder-residue pattern on the victim’s clothing or skin against test patterns made when the suspect weapon is fired at varying distances from a target. A white cloth or a fabric comparable to the victim’s clothing may be used as a test target (see Figure 8–16). Because the spread and density of the residue pattern vary widely between weapons and ammunition, such a comparison is significant only when it is made with the suspect weapon and suspect ammunition, or with ammunition of the same type and make. By comparing the test and evidence patterns, the examiner may find enough similarity in shape and density on which to judge the distance from which the shot was fired.

Without the weapon, the examiner is restricted to looking for recognizable characteristics around the bullet hole. Such findings are at best approximations made as a result of general

WEBEXTRA 8.7 Bullet Standard Helps To Tie Guns To Criminals

distance determination The process of determining the distance between the firearm and a target, usually based on the distribution of powder patterns or the spread of a shot pattern.

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observations and the examiner’s experience. However, some noticeable characteristics should be sought. For instance, when the weapon is held in contact with or less than 1 inch from the target, a heavy concentration of smokelike vaporous lead usually surrounds the bullet entrance hole. Often, loose fibers surrounding a contact hole show scorch marks from the flame discharge of the weapon, and some synthetic fibers may show signs of being melted as a result of the heat from the discharge. Furthermore, the blowback of muzzle gases may produce a stellate (star-shaped) tear pattern around the hole. Such a hole is invariably surrounded by a rim of a smokelike deposit of vaporous lead (see Figure 8–17).

A halo of vaporous lead (smoke) deposited around a bullet hole normally indicates a dis- charge 12 to 18 inches or less from the target. The presence of scattered specks of unburned and partially burned powder grains without any accompanying soot can often be observed at distances up to approximately 25 inches. Occasionally, however, scattered gunpowder particles are noted at a firing distance as far out as 36 inches. With ball powder ammunition, this distance may be extended to 6 to 8 feet.

Finally, a weapon that has been fired more than 3 feet from a target usually does not deposit any powder residues onto the target’s surface. In these cases, the only visual indication that the hole was made by a bullet is a dark ring, known as bullet wipe, around the perimeter of the en- trance hole. Bullet wipe consists of a mixture of carbon, dirt, lubricant, primer residue, and lead wiped off the bullet’s surface as it passes through the target. Again, in the absence of a suspect weapon, these observations are general guidelines for estimating target distances. Numerous factors—barrel length, caliber, type of ammunition, and type and condition of the weapon fired— influence the amount of gunpowder residue deposited on a target.

FIGURE 8–16 Test powder patterns made with a .38 Special Smith & Wesson revolver fired at the following distances from the target: (a) contact, (b) 6 inches, (c) 12 inches, and (d) 18 inches.

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SHOTGUNS The determination of firing distances involving shotguns must again be related to test firings performed with the suspect weapon, using the same type of ammunition known to be used in the crime. In the absence of a weapon, the muzzle-to-target distance can be estimated by measuring the spread of the discharged shot. With close-range shots varying in distance up to 4 to 5 feet, the shot charge enters the target as a concentrated mass, producing a hole somewhat larger than the bore of the barrel. As the distance increases, the pellets progressively separate and spread out. Generally speaking, the spread in the pattern made by a 12-gauge shotgun increases 1 inch for each yard of distance. Thus, a 10-inch pattern would be produced at approximately 10 yards. Of course, this is only a rule of thumb; normally, a great number of variables can affect the shot pattern. Other factors to consider include the barrel length, the size and quantity of the pellets fired, the quantity of powder charge used to propel the pellets, and the choke of the gun under examination. Choke is the degree of constriction placed at the muzzle end of the barrel. The greater the choke, the narrower the shotgun pattern and the faster and farther the pellets will travel.

Powder Residues on Garments When garments or other evidence relevant to a shooting are received in the crime laboratory, the surfaces of all items are first examined microscopically for gunpowder residue. These particles may be identifiable by their characteristic colors, sizes, and shapes. However, the absence of visual indications does not preclude the possibility that gunpowder residue is present. Sometimes the lack of color contrast between the powder and garment or the presence of heavily encrusted deposits of blood can obscure the visual detection of gunpowder. Often, an infrared photograph of the suspect area overcomes the problem. Such a photograph may enhance the contrast, thus revealing vaporous lead and powder particles deposited around the hole (see Figure 8–18). In other situations, this may not help, and the analyst must use chemical tests to detect gunpowder residues.

Nitrites are one type of chemical product that results from the incomplete combustion of smokeless (nitrocellulose) powder. One test method for locating powder residues involves transferring particles embedded on the target surface to chemically treated gelatin-coated pho- tographic paper. This procedure is known as the Greiss test. The examiner presses the photo- graphic paper onto the target with a hot iron; once the nitrite particles are on the paper, they are made easily visible by chemical treatment. In addition, comparing the developed nitrite pattern to nitrite patterns obtained from test firings at known distances can be useful in determining the

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FIGURE 8–17 A contact shot.

choke An interior constriction placed at or near the muzzle end of a shotgun’s barrel to control shot dispersion.

Greiss test A chemical test used to develop patterns of gunpowder residues around bullet holes.

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shooting distance from the target. A second chemical test is then performed to detect any trace of lead residue around the bullet hole. The questioned surface is sprayed with a solution of sodium rhodizonate, followed by a series of oversprays with acid solutions. This treatment causes lead particles to exhibit a pink color, followed by a blue-violet color.

Primer Residues on the Hands The firing of a weapon not only propels residues toward the target, but also blows gunpowder and primer residues back toward the shooter (see Figure 8–19). As a result, traces of these residues are often deposited on the firing hand of the shooter, and their detection can provide valuable information as to whether an individual has recently fired a weapon.

Detecting Primer Residues Early efforts at demonstrating powder residues on the hands centered on chemical tests that could detect unburned gunpowder or nitrates. For many years, the dermal nitrate test enjoyed popular- ity. It required the application of hot paraffin or wax to the suspect’s hand with a paintbrush. After drying into a solid crust, the paraffin was removed and tested with diphenylamine. A blue color was taken as an indication of a positive reaction for nitrates. However, the dermal nitrate test has fallen into disfavor with law enforcement agencies, owing mainly to its lack of specificity. Com- mon materials such as fertilizers, cosmetics, urine, and tobacco all give positive reactions that are indistinguishable from that obtained for gunpowder by this test.

Efforts to identify a shooter now center on the detection of primer residues deposited on the hand of a shooter at the time of firing. With the exception of most .22-caliber ammunition, prim- ers currently manufactured contain a blend of lead styphnate, barium nitrate, and antimony sul- fide. Residues from these materials are most likely to be deposited on the thumb web and the back of the firing hand of a shooter because these areas are closest to gases escaping along the side or back of the gun during discharge. In addition, individuals who handle a gun without firing it may have primer residues deposited on the palm of the hand coming in contact with the weapon.

However, with the handling of a used firearm, the passage of time, and the resumption of normal activities following a shooting, gunshot residues from the back of the hand are frequently

(a) (b)

FIGURE 8–18 (a) A shirt bearing a powder stain, photographed under normal light. (b) An infrared photograph of the same shirt.

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redistributed to other areas, including the palms. Therefore, it is not unusual to find higher levels of barium and antimony on the palms than on the backs of the hands of known shooters. Another possibility is the deposition of significant levels of barium and antimony on the hands of an individual who is near a firearm when it is discharged.

Tests for Primer Residues Determination of whether a person has fired or handled a weapon or has been near a discharged firearm is normally made by measuring the presence and possibly the amount of barium and antimony on the relevant portions of the suspect’s hands. A variety of materials and techniques are used for removing these residues. The most popular approach, and certainly the most convenient for the field investigator, requires the application of an adhesive tape or adhesive to the hand’s surface in order to remove any adhering residue particles.

SWABBING Another approach is to remove any residues present by swabbing both the firing and nonfiring hands with cotton that has been moistened with 5 percent nitric acid. The front and back of each hand are separately swabbed. All four swabs, along with a moistened control, are then forwarded to the crime laboratory for analysis (see Appendix II for a detailed description of residue collection procedures).

In any case, once the hands are treated for the collection of barium and antimony, the col- lection medium must be analyzed for the presence of these elements. High barium and antimony levels on the suspect’s hand(s) strongly indicate that the person fired or handled a weapon or was near a firearm when it was discharged. Because these elements are normally present after a firing in small quantities (less than 10 micrograms), only the most sensitive analytical techniques can detect them.

Unfortunately, even though most specimens submitted for this type of analysis have been from individuals strongly suspected of having fired a gun, there has been a low rate of posi- tive findings. The major difficulty appears to be the short time that primer residues remain on the hands. These residues are readily removed by intentional or unintentional washing, rubbing, or wiping of hands. In fact, one study convincingly demonstrated that it is diffi- cult to detect primer residues on cotton hand swabs taken as soon as two hours after firing

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FIGURE 8–19 When a handgun is fired, gunpowder and primer residues are normally blown back toward the hand of the shooter.

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a weapon.2 Hence, some laboratories do not accept cotton hand swabs taken from living sub- jects six or more hours after a firing has occurred.

In cases that involve suicide victims, a higher rate of positives for the presence of gunshot residue is obtained when the hand swabbing is conducted before the person’s body is moved or when the hands are protected by paper bags.3 However, hand swabbing or the application of an adhesive cannot be used to detect firings with most .22-caliber rim-fire ammunition. Such am- munition may contain only barium or neither barium nor antimony in its primer composition.

SEM TESTING Most laboratories possessing gunshot residue detection capabilities require the application of an adhesive to the shooter’s hands. Microscopic primer and gunpowder particles on the adhesive are then located with the aid of a scanning electron microscope (SEM) (see Figure 8–20). These particles have a characteristic size and shape that readily distinguish them from other contaminants present on the hands (see Figure 8–21). When the SEM is linked to an X-ray analyzer (see page 162), an elemental analysis of the particles can be conducted. A finding of a select combination of elements (lead, barium, and antimony) confirms that the particles could be primer residue (see Figure 8–22). A complication to the interpretation of the significance of these

2 J. W. Kilty, “Activity after Shooting and Its Effect on the Retention of Primer,” Journal of Forensic Sciences 29 (1975): 219.

3 G. E. Reed et al., “Analysis of Gunshot Residue Test Results in 112 Suicides,” Journal of Forensic Sciences 35 (1990): 62.

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FIGURE 8–21 An SEM view of gunshot residue particles.

FIGURE 8–20 (a) Adhesive stubs used to sample a suspect’s shooter’s hands. (b) Sampling a suspect’s hand for gunshot residue with an adhesive stub.

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findings is that brake linings and fireworks have been reported to yield particles indistinguishable from gunshot residue. Interestingly, bullet manufacturers are moving in the direction of removing lead from bullets, thus further complicating the characterization of primer residue. Appendix I contains a detailed description of the SEM residue collection procedure.

The major advantage of the SEM approach for primer residue detection is its enhanced specificity over hand swabbing. The SEM characterizes primer particles by their size and shape as well as by their chemical composition. Unfortunately, the excessive operator time required to search out and characterize gunshot residue has deterred the use of this technique. The availabil- ity of automated particle search and identification systems for use with scanning electron micro- scopes may overcome this problem. Results of work performed with automated systems show it to be significantly faster than a manual approach for searching out gunshot residue particles.

Serial Number Restoration Today, many manufactured items, including automobile engine blocks and firearms, are im- pressed with a serial number for identification. Increasingly, the criminalist is asked to restore such a number when it has been removed or obliterated by grinding, rifling, or punching.

Serial numbers are usually stamped on a metal body or frame, or on a plate, with hard steel dies. These dies strike the metal surface with a force that allows each digit to sink into the metal at a prescribed depth. Serial numbers can be restored because the metal crystals in the stamped zone are placed under a permanent strain that extends a short distance beneath the original numbers. When a suitable etching agent is applied, the strained area dissolves faster than the unaltered metal, thus revealing the etched pattern in the form of the original numbers (see Figure 8–23). However, if the zone of strain has been removed, or if the area has been impressed with a different strain pattern, the number usually cannot be restored.

0 2 4 6 8 10 12 14 16 18 20

Range (ke V)

Pb Counts [x10]

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FIGURE 8–22 Spectrum showing the presence of lead, barium, and antimony in gunshot residue.

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Before any treatment with the etching reagent, the obliterated surface must be thoroughly cleaned of dirt and oil and polished to a mirrorlike finish. The reagent is swabbed onto the surface with a cotton ball. The choice of etching reagent depends on the type of metal surface being worked on. A solution of hydrochloric acid (120 mL), copper chloride (90 g), and water (100 mL) generally works well for steel surfaces.

Collection and Preservation of Firearms Evidence Firearms The Hollywood image of an investigator picking up a weapon by its barrel with a pencil or stick in order to protect fingerprints must be avoided. This practice only disturbs powder deposits, rust, or dirt lodged in the barrel, and consequently may alter the striation markings on test-fired bullets. If recovery of latent fingerprints is a primary concern, hold the weapon by the edge of the trigger guard or by the checkered portion of the grip, which usually does not retain identifiable fingerprints.

The most important consideration in handling a weapon is safety. Before any weapon is sent to the laboratory, all precautions must be taken to prevent an accidental discharge of a loaded weapon in transit. In most cases, it will be necessary to unload the weapon. If this is done, a record should first be made of the weapon’s hammer and safety position; likewise, the location of all fired and unfired ammunition in the weapon must be recorded.

When a revolver is recovered, the chamber position in line with the barrel should be in- dicated by a scratch mark on the cylinder. Each chamber is designated with a number on a diagram, and as each cartridge or casing is removed, it should be marked to correspond to the numbered chambers in the diagram. Knowledge of the cylinder position of a cartridge casing may be useful for later determination of the sequence of events, particularly in shooting cases

FIGURE 8–23 Obliterated or altered serial numbers on firearms can be restored by analysts using chemical means.

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when more than one shot was fired. Place each round in a separate box or envelope. If the weapon is an automatic, the magazine must be removed and checked for prints and the chamber then emptied.

As with any other type of physical evidence recovered at a crime scene, firearms evidence must be marked for identification and a chain of custody must be established. Therefore, when a firearm is recovered, an identification tag should be attached to the trigger guard. The tag should be marked to show appropriate identifying data, including the weapon’s serial number, make, and model and the investigator’s initials. Place the unloaded firearm into a ridged box properly labeled for shipment to the examining forensic facility.

When a weapon is recovered from an underwater location, no effort must be made to dry or clean it. Instead, the firearm should be transported to the laboratory in a receptacle containing enough of the same water necessary to keep it submerged. This procedure prevents rust from developing during transport.

Ammunition Protection of class and individual markings on bullets and cartridge cases must be the primary concern of the field investigator. Thus, extreme caution is needed when removing a lodged bullet from a wall or other object. If the bullet’s surface is accidentally scratched during this operation, valuable striation markings could be obliterated. It is best to free bullets from their target by carefully breaking away the surrounding support material while avoiding direct contact with the projectile.

Bullets, cartridge casings, and discharged shells from shotguns should just be placed in a container that is appropriately marked for identification. It is recommended that the investigator not directly mark these items with a scribe. In any case, the investigator must protect the bullet by wrapping it in tissue paper before placing it in a pillbox or an envelope for shipment to the crime laboratory. Minute traces of evidence such as paint and fibers may be adhering to the bullet; the investigator must take care to leave these trace materials intact.

When semiautomatic or automatic weapons have been fired, the ejection pattern of the cas- ings can help establish the relationship of the suspect to his or her victim. For this reason, the exact location of the place from which a shell casing was recovered is important information that must be noted by the investigator.

In incidents involving shotguns, any wads recovered are to be packaged and sent to the labo- ratory. An examination of the size and composition of the wad may reveal information about the type of ammunition used and the gauge of the shotgun.

Gunpowder Deposits The clothing of a firearms victim must be carefully preserved so as to prevent damage or disrup- tion to powder residues deposited around a bullet or shell hole. The cutting or tearing of clothing in the area of the holes must be avoided as the clothing is being removed. All wet clothing should be air-dried out of direct sunlight and then folded carefully so as not to disrupt the area around the bullet hole. Each item should be placed in a separate paper bag.

Tool Marks A tool mark is any impression, cut, gouge, or abrasion caused by a tool coming into contact with another object. Most often, tool marks are encountered at burglary scenes that involve forcible entry into a building or safe. Generally, these marks occur as indented impressions into a softer surface or as abrasion marks caused by the tool cutting or sliding against another object.

Comparing Tool Marks Typically, an indented impression is left on the frame of a door or window as a result of the prying action of a screwdriver or crowbar. A careful examination of these impressions can reveal impor- tant class characteristics—that is, the size and shape of the tool. However, they rarely reveal any significant individual characteristics that could permit the examiner to individualize the mark to a

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single tool. Such characteristics, when they do exist, usually take the form of discernible random nicks and breaks that the tool has acquired through wear and use (Figure 8–24).

Just as the machined surfaces of a firearm are impressed with random striations during its manufacture, the edges of a pry bar, chisel, screwdriver, knife, or cutting tool likewise display a series of microscopic irregularities that look like ridges and valleys. Such markings are left as a result of the machining processes used to cut and finish tools. The shape and pattern of such min- ute imperfections are further modified by damage and wear during the life of the tool. Consider- ing the unending variety of patterns that the hills and valleys can assume, it is highly unlikely that any two tools will be identical. Hence, these minute imperfections impart individuality to each tool.

If the edge of a tool is scraped against a softer surface, it may cut a series of striated lines that reflect that pattern of the tool’s edge. Markings left in this manner are compared in the laboratory through a comparison microscope with test tool marks made from the suspect tool. The result can be a positive comparison, and hence a definitive association of the tool with the evidence mark, when a sufficient quantity of striations match between the evidence and test markings.

One of the major problems associated with tool mark comparisons is the difficulty in dupli- cating in the laboratory the tool mark left at the crime scene. A thorough comparison requires the preparation of a series of test marks obtained by applying the suspect tool at various angles and pressures to a soft metal surface (lead is commonly used). This approach gives the examiner ample opportunity to duplicate many of the details of the original evidence marking. A photomi- crograph of a typical tool mark comparison is illustrated in Figure 8–25.

Collecting Tool Mark Evidence Whenever practical, the entire object or the part of the object bearing a tool mark should be sub- mitted to the crime laboratory for examination. When removal of the tool mark is impractical, the only recourse is to photograph the marked area to scale and make a cast of the mark. Under these circumstances, liquid silicone casting material has been found to be the most satisfactory for reproducing most of the fine details of the mark. See Figure 8–26. However, even under the most optimum conditions, the clarity of many of the tool mark’s minute details will be lost or

FIGURE 8–24 A comparison of a tool mark with a suspect screwdriver. Note how the presence of nicks and breaks on the tool’s edge helps individual- ize the tool to the mark.

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obscured in a photograph or cast. Of course, this will reduce the chance of individualizing the mark to a single tool.

The crime-scene investigator must never attempt to fit the suspect tool into the tool mark. Any contact between the tool and the marked surface may alter the mark and will, at the least, raise serious questions about the integrity of the evidence. The suspect tool and mark must be packaged in separate containers, with every precaution taken to avoid contact between the tool or mark and another hard surface. Failure to properly protect the tool or mark from damage could result in the destruction of its individual characteristics.

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FIGURE 8–26 (a) Casting a tool mark impression with a silicone-based putty. (b) Impression alongside suspect tool.

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FIGURE 8–25 A photograph of a tool mark comparison seen under a comparison microscope.

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Furthermore, the tool or its impression may contain valuable trace evidence. Chips of paint adhering to the mark or tool provide perhaps the best example of how the transfer of trace physi- cal evidence can occur as a result of using a tool to gain forcible entry into a building. Obvi- ously, the presence of trace evidence greatly enhances the evidential value of the tool or its mark and requires special care in handling and packaging the evidence to avoid losing or destroying these items.

Other Impressions From time to time, impressions of another kind are left at a crime scene. This evidence may take the form of a shoe, tire, or fabric impression and may be as varied as a shoe impression left on a piece of paper at the scene of a burglary (Figure 8–27), or when a hit-and-run victim’s garment has come into violent contact with an automobile (Figure 8–28), or an impression of a bloody shoe print left on a carpet and visualized by luminal (see Figure 8–29 a and b).

Preserving Impressions The primary consideration in collecting impressions at the crime scene is the preservation of the impression or its reproduction for later examination in the crime laboratory. Before any impres- sion is moved or otherwise handled, it must be photographed (a scale should be included in the picture) to show all the observable details of the impression. Several shots should be taken di- rectly over the impression as well as at various angles around the impression. The skillful use of side lighting for illumination will help highlight many ridge details that might otherwise remain obscured. Photographs should also be taken to show the position of the questioned impression in relation to the overall crime scene.

Although photography is an important first step in preserving an impression, it must be considered merely a backup procedure that is available to the examiner if the impression is

(a)

FIGURE 8–27 (a) Impression of shoe found at a crime scene. (b) Test impression made with suspect shoe. A sufficient number of points of comparison exist to support the conclusion that the suspect shoe left the impression at the crime scene.

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FIGURE 8–28 A pattern impression on a car bumper arising from a hit-and-run. Note rivets from the jeans are present in the impression. The writing from the rivet on the right side of the bumper is visible.

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damaged before reaching the crime laboratory. Naturally, it is preferable for the examiner to receive the original impression for comparison to the suspect shoe, tire, garment, and so forth. In most cases when the impression is on a readily recoverable item, such as glass, paper, or floor tile, little or no difficulty is presented in transporting the evidence intact to the laboratory.

Lifting Impressions If an impression is encountered on a surface that cannot be submitted to the laboratory, the inves- tigator may be able to preserve the print in a manner that is analogous to lifting a fingerprint. This is especially true of impressions made in light deposits of dust or dirt. A lifting material large enough to lift the entire impression should be used. Carefully place the lifting material over the entire impression. Use a fingerprint roller to eliminate any air pockets before lifting the impres- sion off the surface.

A more exotic approach to lifting and preserving dust impressions involves the use of a portable electrostatic lifting device. The principle employed is similar to that of creating an electrostatic charge on a comb and using the comb to lift small pieces of tissue paper. A sheet of mylar film is placed on top of the dust mark, and the film is pressed against the impression with the aid of a roller. The high-voltage electrode of the electrostatic unit is then placed in contact with the film while the unit’s earth electrodes are placed against a metal plate (earth plate) (see Figure 8–30). A charge difference develops between the mylar film and the surface below the dust mark so that the dust is attached to the lifting film. In this manner, dust prints on chairs, walls, floors, and the like, can be transferred to the mylar film. Floor surfaces up to 40 feet long can be covered with a mylar sheet and searched for dust impressions. The electrostatic lifting technique is particularly helpful in recovering barely visible dust prints on colored surfaces. Dust impressions can also be enhanced through chemical development (see Figure 8–31).

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Casting Impressions Shoe and tire marks impressed into soft earth at a crime scene are best preserved by photography and casting. Class I dental stone, a form of gypsum, is widely recommended for making casts of shoe and tire impressions. The cast should be allowed to air-dry for 24 to 48 hours before it is shipped to the forensic science laboratory for examination. Figure 8–32 illustrates a cast made from a shoe print in mud. The cast compares to the suspect shoe.

FIGURE 8–29 (a) A section of a carpet under normal light showing a faint footprint in blood. (b) Same section of the carpet after spraying with luminal.

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FIGURE 8–30 Electrostatic lifting of a dust impression off a floor using an electrostatic unit.

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An aerosol product known as Snow Impression Wax is available for casting snow impres- sions. The recommended procedure is to spray three light coats of the wax at an interval of one to two minutes between layers, and then let it dry for ten minutes. A viscous mixture of Class I dental stone is then poured into the wax-coated impression. After the casting material has hard- ened, the cast can be removed.

Several chemicals can be used to develop and enhance footwear impressions made with blood. In areas where a bloody footwear impression is very faint or where a subject has tracked through blood, leaving a trail of bloody impressions, chemical enhancement can visualize latent or nearly invisible footwear impressions. A number of chemical formulas useful for bloody foot- wear impression analysis are listed in Appendix IV.

Several blood enhancement chemicals have been examined for their impact on short tan- dem repeat (STR) DNA typing. (This particular method of DNA analysis will be discussed in Chapter 15.) None of the chemicals examined had a deleterious effect, on a short-term basis, on the ability to carry out STR DNA typing on the blood.4

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FIGURE 8–31 (a) A dust impression of a shoe print on cardboard before enhancement. (b) Shoe print after chemical enhancement with Bromophenol Blue and exposure to water vapor.

4 C. J. Frégeau et al., “Fingerprint Enhancement Revisited and the Effects of Blood Enhancement Chemicals on Subsequent Profiler Plus™ Fluorescent Short Tandem Repeat DNA Analysis of Fresh and Aged Bloody Fingerprints,” Journal of Forensic Sciences 45 (2000): 354.

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Comparing Impressions Whatever the circumstances, the laboratory procedures used to examine any type of impression remain the same. Of course, a comparison is possible only when the item suspected of having made the impression is recovered. Test impressions may be necessary to compare the character- istics of the suspect item with the evidence impression.

The evidential value of the impression is determined by the number of class and individual characteristics that the examiner finds. Agreement with respect to size, shape, or design may permit the conclusion that the impression could have been made by a particular shoe, tire, or garment, but one cannot entirely exclude other possible sources from having the same class char- acteristics. More significant is the existence of individual characteristics arising out of wear, cuts, gouges, or other damage. A sufficient number or the uniqueness of such points of comparison supports a finding that both the evidence and test impressions originated from only one source.

When a tire tread impression is left at a crime scene, the laboratory can examine the design of the impression and possibly determine the style and/or manufacturer of the tire. This may be particularly helpful to investigators when a suspect tire has not yet been located.

New computer software may help the forensic scientist compare shoe prints. For ex- ample, an automated shoe print identification system developed in England, called shoeprint image capture and retrieval (SICAR), incorporates multiple databases to search known and unknown footwear files for comparison against footwear specimens. Using the system, an impression from a crime scene can be compared to a reference database to find out what type of shoe caused the imprint. That same impression can also be searched in the suspect and crime databases to reveal whether that shoe print matches the shoes of a person who has been in custody or the shoe prints left behind at another crime scene. When matches are made dur- ing the searching process, the images are displayed side by side on the computer screen (see Figure 3–8 in Chapter 3).

Human bite marks on skin and foodstuffs have been important items of evidence for convict- ing defendants in a number of homicide and rape cases in recent years. If a sufficient number of points of similarity between test and suspect bite marks are present, a forensic odontologist may conclude that a bite mark was made by a particular individual (see Figure 8–33).

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FIGURE 8–32 (a) Shoe impression in mud. (b) Cast of shoe impression. (c) Shoe suspected of leaving muddy impression.

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WEBEXTRA 8.8 Casting a Footwear Impression

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Procedure 1. Retrieve any fragments or debris that are not im-

bedded within the impression. Photograph the im- pression before and after retrieving debris; include a ruler in the photograph. A frame for containing the dental stone may be installed around an impres- sion that is shallow or located on an inclined surface.

2. To solidify the soil, a fixative such as hair spray is used (see [a]). Hold the can of hair spray about 18 inches from the soil within the impression. Very lightly, spray an even layer over the impression, using a sweeping motion and taking care to avoid any damage to the impression.

3. Wait ten minutes to allow the hair spray to dry. 4. Add an appropriate amount of water to a premea-

sured amount of dental stone (see [b]). Add water in increments. The usual amount is about 10 to 12 fluid ounces of water to about 1.5 to 2 pounds of dental stone. If using a zip-top bag, seal the bag and mix by working back and forth with your fin- gers for at least three minutes (see [c]). Mix until a pancake-batter-like consistency is reached.

Casting Footwear and Tire Impressions

Footwear and tire impressions may be found at any type of crime scene and can provide a primary means to identify or exclude a suspect. The preferred method of collection for this type of evidence is cast- ing the impression—that is, making a mold and pre- serving it for analysis in the lab. When a footwear or tire impression is found in dirt at the crime scene, the casting process is as follows:

Materials Ruler One small can of aerosol hair spray 1-gallon zip-top bag Paint stirrer or large, long-handled spoon Carton of dental stone Water Camera Plastic or metal casting frame (optional)

inside the science

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FIGURE 8–33 Upper dental model from the teeth of the suspect matches the individual teeth characteristics of the bite marks.

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(e)

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7. When the cast no longer adheres to the soil and is relatively dry (usually about one hour), remove the cast. If necessary, the cast can be dug out from the sides.

8. Store the cast for 48 hours to allow it to dry com- pletely. If a cast is not allowed to dry long enough, some ridge details may disappear.

9. Once the cast is dry, rinse any loose soil from it with softly running water. A soft-bristled brush may also be used. Do not scrub or pick off any- thing. Pat dry with paper towels.

5. Open one corner of the bag. Pour the dental stone through the opening onto the ground beside the impression and allow it to carefully run into the im- pression. Use a paint stirrer, a spoon, or a gloved hand as a medium to disperse the stream so it does not destroy the fine details of the impres- sion (see [d]). Continue pouring until the dental stone completely fills the impression (see [e]) and reaches at least 1⁄2 inch in thickness. If necessary, additional casting material may be poured over the top of the original cast to add thickness.

6. Label the wet plaster surface with the date, ini- tials, and any other information required for evi- dence labeling.

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Structural variations and irregularities caused by scratches, nicks, breaks, and wear permit the criminalist to relate a bullet to a gun, a scratch or abrasion mark to a single tool, or a tire track to a particular automobile.

The manufacture of a barrel requires impressing its in- ner surface with spiral grooves, a step known as rifling. The surfaces of the original bore remaining between the grooves are called lands. No two rifled barrels, even those manufac- tured in succession, have identical striation markings. These striations form the individual characteristics of the barrel. The inner surface of the barrel of a gun leaves its striation markings on a bullet passing through it. The number of lands and grooves and their direction of twist are obvious points

of comparison during the initial stages of an examination. Any differences in these class characteristics immediately eliminate the possibility that both bullets traveled through the same barrel.

The comparison microscope is the most important tool to a firearms examiner. Two bullets can be observed and com- pared simultaneously within the same field of view. Not only must the lands and grooves of the test and evidence bullet have identical widths, but the longitudinal striations on each must coincide. The firing pin, breechface, and ejector and extractor mechanism also offer a highly distinctive signature for indi- vidualization of cartridge cases. The advent of computerized imaging technology has made possible the storage of bullet

chapter summary

The O. J. Simpson Trial— Who Left the Impressions at the Crime Scene?

On the night of June 12, 1994, Nicole Brown—ex-wife of foot- ball star O. J. Simpson—and her friend Ron Goldman were brutally murdered on the grounds outside her home in Brent- wood, California. O. J. Simpson was arrested for their murders but professed his innocence. At the crime scene, investigators found bloody shoe impressions along the concrete walkway leading up to the front door of Brown’s condominium. These shoe impressions were of extremely high quality and of in- tricate detail. The news media broadcast countless images of these bloody shoe prints on television, making it obvious to the killer that those shoes would surely link him to the crime.

Famed FBI shoe print examiner William J. Bodziak in- vestigated the footwear evidence from the scene. His first task was to identify the brand of shoe that made the marks. Because the pattern was clear and distinct, with complete toe-to-heel detail, this seemed a simple task at first. Bodziak compared this pattern to the thousands of sole patterns in the FBI’s data- base. None matched. He then went to his reference collection of books and trade show brochures, again with no success.

Bodziak’s experience told him that these were expensive, Italian-made casual dress shoes with a sole made from syn- thetic material. Using this knowledge, he shopped the high- end stores for a similar tread pattern but still was unable to identify the shoes. He then drew a composite sketch of the sole and faxed the image to law enforcement agencies and shoe

manufacturers and distributors worldwide. The owner of the American distributing company for Bruno Magli shoes was the only one to respond.

Further exhaustive investigation revealed that these were extremely rare shoes. There were two styles of shoe bearing this exact sole design. They were available for only two years, and from a mere forty stores in the United States and Puerto Rico. The Lorenzo style shoe had a bootlike upper that came to the ankle. The Lyon style shoe had the lower, more typical dress shoe cut. The impressions were made by a size 12 shoe, and it was later determined that only 299 pairs of size 12 with this tread pattern were sold in the United States.

Simpson flatly denied ever owning these shoes, adding that he would never wear anything so ugly. However, he was known to wear a size 12, and photographs taken almost nine months before the murders show Simpson wearing a pair of black leather Bruno Magli Lorenzo shoes. These shoes were available in several colors, so this narrows the number of shoes matching Simpson’s pair of Lorenzos (this size, color, and style) sold in the United States to twenty-nine pairs.

Proving that Simpson owned a pair of shoes that had the exact pattern found printed in blood at the crime scene was an essential component of the case, but it was not done in time to be used during the criminal prosecution. The photographs of Simpson in his Bruno Magli shoes were released after the cul- mination of the criminal trial, so the jury never heard the direct evidence that Simpson owned these shoes. However, this proved to be an important link uniting Simpson with the crime scene in the civil trial. Although O. J. Simpson was acquitted of the mur- ders of Nicole Brown and Ron Goldman in the criminal trial, he was judged responsible for their murders in the civil court case.

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and cartridge surface characteristics in a manner analogous to automated fingerprint files. However, the final comparison will be made by the forensic examiner through traditional mi- croscopic methods.

The distribution of gunpowder particles and other dis- charge residues around a bullet hole permits an assessment of the distance from which a handgun or rifle was fired. The firing of a weapon not only propels residues toward the target, but also blows gunpowder and primer residues back toward the shooter. As a result, traces of these residues are often deposited on the firing hand of the shooter, and their detection can provide valuable information as to whether an individual has recently fired a weapon. Examiners measure the amount of barium and antimony on the relevant portion of the suspect’s hands or characterize the morphology of par- ticles containing these elements to determine whether a per- son has fired or handled a weapon, or was near a discharged firearm.

Increasingly, the criminalist is asked to restore a se- rial number that has been obliterated by grinding, rifling, or punching. Restoration of serial numbers is possible through

chemical etching because the metal crystals in the stamped zone are placed under a permanent strain that extends a short distance beneath the original numbers.

A tool mark is any impression, cut, gouge, or abrasion caused by a tool coming into contact with another object. Hence, any minute imperfections on a tool impart indi- viduality to that tool. The shape and pattern of such imper- fections are further modified by damage and wear during the life of the tool. The comparison microscope is used to compare crime-scene tool marks with test impressions made with the suspect tool. When shoe and tire marks are impressed into soft earth at a crime scene, their preserva- tion is best accomplished by photography and casting. In areas where a bloody footwear impression is very faint or where the subject has tracked through blood, leaving a trail of bloody impressions, chemical enhancement can visualize latent or nearly invisible blood impressions. A sufficient number of points of comparison or the unique- ness of such points support a finding that both the ques- tioned and test impressions originated from one and only one source.

review questions

1. The ___________ is the original part of the bore left after rifling grooves are formed.

2. The diameter of the gun barrel is known as its ___________.

3. True or False: The number of lands and grooves is a class characteristic of a barrel. ___________

4. The ___________ characteristics of a rifled barrel are formed by striations impressed into the barrel’s surface.

5. The most important instrument for comparing bullets is the ___________.

6. To make a match between a test bullet and a recovered bullet, the lands and grooves of the test and evidence bullet must have identical widths, and the longitudinal ___________ on each must coincide.

7. True or False: It is always possible to determine the make of a weapon by examining a bullet it fired. ___________

8. A shotgun has a(n) ___________ barrel.

9. The diameter of a shotgun barrel is expressed by the term ___________.

10. True or False: Shotgun pellets can be individualized to a single weapon. ___________

11. True or False: A cartridge case can be individualized to a single weapon. ___________

12. The automated firearms search system developed by the FBI and ATF as a unified system incorporating both

DRUGFIRE and IBIS technologies available in prior years is known as ___________.

13. True or False: The distribution of gunpowder particles and other discharge residues around a bullet hole per- mits an approximate determination of the distance from which the gun was fired. ___________

14. True or False: Without the benefit of a weapon, an examiner can make an exact determination of firing distance. ___________

15. A halo of vaporous lead (smoke) deposited around a bullet hole normally indicates a discharge ___________ to ___________ inches from the target.

16. If a firearm has been fired more than 3 feet from a tar- get, usually no residue is deposited but a dark ring, known as ___________, is observed.

17. As a rule of thumb, the spread in the pattern made by a 12-gauge shotgun increases 1 inch for every ___________ of distance from the target.

18. A(n) ___________ photograph may help visualize gun- powder deposits around a target.

19. True or False: One test method for locating powder res- idues involves transferring particles embedded on the target surface to chemically treated photographic paper. ___________

20. Current methods for identifying a shooter rely on the detection of ___________ residues on the hands.

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28. True or False: Cartridge cases are best marked at the base of the shell. ___________

29. The clothing of the victim of a shooting must be han- dled so as to prevent disruption of ___________ around bullet holes.

30. A(n) ___________ is any impression caused by a tool coming into contact with another object.

31. Tool marks compare only when a sufficient number of ___________ match between the evidence and test markings.

32. Objects bearing tool marks should be submitted intact to the crime lab or a(n) ___________ should be taken of the tool mark.

33. An imprint may be lifted using lifting sheets or a(n) ___________.

35. Shoe and tire marks impressed into soft earth at a crime scene are best preserved by ___________ and ___________.

35. A wear pattern, cut, gouge, or other damage pattern can impart ___________ characteristics to a shoe.

21. Determining whether an individual has fired a weapon is done by measuring the elements ___________ and ___________ present on the hands.

22. True or False: Firings with all types of ammunition can be detected by hand swabbings with nitric acid. ___________

23. Microscopic primer and gunpowder particles on the adhesives applied to a suspected shooter’s hand can be found with a(n) ___________.

24. True or False: Restoration of serial numbers is possible because in the stamped zone the metal is placed under a(n) permanent strain that extends beneath the original numbers. ___________

25. True or False: It is proper to insert a pencil into the barrel when picking up a crime-scene gun. ___________

26. Recovered bullets are initialed on either the ___________ or ___________ of the bullet.

27. True or False: Because minute traces of evidence such as paint and fibers may be adhering to a recovered bul- let, the investigator must take care to remove these trace materials immediately. ___________

application and critical thinking

c. 6 yards

d. 30 yards

3. Criminalist Ben Baldanza is collecting evidence from the scene of a shooting. After locating the revolver sus- pected of firing the shots, Ben picks the gun up by the grip, unloads it, and places the ammunition in an enve- lope. He then attaches an identification tag to the grip. Searching the scene, Ben finds a bullet lodged in the wall. He uses pliers to grab the bullet and pull it from the wall, then inscribes the bullet with his initials and places it in an envelope. What mistakes, if any, did Ben make in collecting this evidence?

4. How would you go about collecting impressions in each of the following situations?

a. You discover a shoe print in dry dirt.

b. You discover a tool mark on a windowsill.

c. You discover tire marks in soft earth.

d. You discover a shoe print on a loose piece of tile.

e. You discover a very faint shoe print in dust on a col- ored linoleum floor.

1. From each of the following descriptions of bullet holes, use general guidelines to estimate the distance from the shooter to the target.

a. A few widely scattered gunpowder particles with no soot around the entrance hole

b. A dark ring around the bullet hole, but no soot or gunpowder particles

c. A halo of soot surrounding the entrance hole along with scattered specks of powder grains

d. Scorch marks and melted fibers surrounding the en- trance hole

2. You are investigating a shooting involving a 12-gauge shotgun with a moderately high choke. The spread of the pattern made by the pellets measures 12 inches. In your opinion, which of the following is probably closest to the distance from the target to the shooter? Explain your answer and explain why the other answers are likely to be incorrect.

a. 18 yards

b. 12 yards

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further references

(A) (B)

5. Gunshot residue patterns (A) through (D) (contact, 1 inch, 6 inches, and 18 inches) from a 40-caliber pistol are shown in the figures. Match the firing distance to each pattern.

Bodziak, William J., Footwear Impression Evidence, 2nd ed. Boca Raton, Fla.: CRC Press, 2000.

Bodziak, William J., Tire Tread and Tire Track Evidence: Recovery and Forensic Examination. Boca Raton, Fla.: CRC Press, 2008.

Heard, B. J., Handbook of Firearms and Ballistics: Examining and Interpreting Forensic Evidence. 2nd ed. Chichester, West Sussex, U.K., 2008.

Hilderbrand, Dwane S., Footwear: The Missed Evidence, 2nd ed. Wildomar, Calif.: Staggs, 2007.

An Introduction to Forensic Firearm Identification, http:// www.firearmsid.com/

Rowe, Walter F., “Firearms Identification,” in R. Saferstein, ed., Forensic Science Handbook, vol. 2, 2nd ed. Upper Saddle River, N.J.: Prentice Hall, 2005.

Schehl, S. A., “Firearms and Toolmarks in the FBI Labora- tory,” Forensic Science Communications 2, no. 2 (2000), http://www.fbi.gov/about-us/lab/forensic-science- communications/fsc/april2000/index.htm/schehl1.htm

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Ted Bundy, Serial Killer

The name Ted Bundy is synonymous with the term serial killer. This handsome, gregarious, and worldly onetime law student is believed to be responsible for 40 murders between 1964 and 1978. His reign of terror stretched from the Pacific Northwest down into California and into Utah, Idaho, and Colorado, finally ending in Florida. His victims were typically young women, usually murdered with a blunt instrument or by strangulation and sexually assaulted before and after death. First convicted in Utah in 1976 on a charge of kidnapping, Bundy managed to escape after his extradition to Colorado on a murder charge. Ultimately, Bundy found his way to the Tallahassee area of Florida. There he unleashed mayhem, killing two women at a Florida State University sorority house and then murdering a 12-year-old girl three weeks later. Fortunately, future victims were spared when Bundy was arrested while driving a stolen vehicle.

As police investigated the sorority murders, they noted that one victim, who had been beaten over

the head with a log, raped, and strangled, also had bite marks on her left buttock and breast.

Supremely confident that he could beat the sorority murder charges, the arrogant Bundy insisted on acting as his own attorney. His unfounded optimism was shattered in the courtroom when a forensic odontologist matched the bite mark on the victim’s buttock to Bundy’s front teeth. Bundy was ultimately executed in 1989.

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