The Difference Between Preliminary Field and Laboratory Testing

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1Forensic Science and Criminalistics

Associated Press

Learning Objectives After reading this chapter, you should be able to do the following:

▪ Define forensic science and how it contributes to a case, as well as explain the CSI Effect and the scientific method.

▪ Summarize the history of forensic science and contributors to the field.

▪ List and describe some forensic science specialties.

▪ Identify the elements of a forensic investigation, how physical evidence can be produced, and forensic analysis.

▪ Describe the work and work product of a forensic scientist.

▪ Describe the U.S. court system, and the key rulings on physical evidence admissibility through expert testimony.

▪ List and discuss major issues in forensic science today.

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8Pattern Evidence I: General Patterns and Fingerprints

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Learning Outcomes After reading this chapter, you should be able to

▪ Describe pattern evidence that can be used for identification, individualization, and reconstruction.

▪ Explain the collection and preservation of pattern evidence.

▪ Explain how pattern evidence is analyzed.

▪ Summarize the nature and history of fingerprints and their role in personal identification.

▪ Discuss how fingerprint evidence is collected and preserved.

▪ Explain how fingerprints are analyzed.

Section 8.1Classification of Pattern Evidence

Introduction In this chapter and in Chapters 9 and 10, we will discuss pattern evidence. As we mentioned in Chapter 1, identification, individualization, and reconstruction can be major aspects of a forensic case or a forensic investigation. Many of the topics in the next two chapters concern patterns for individualization, including physical patterns, fingerprints, footprints, footwear and tire impressions, handwriting, firearms and tool mark identification, and bite marks. Bloodstain patterns are reconstruction patterns, and we discuss this topic in Chapter 10.

This chapter looks closely at physical patterns (broken or torn objects) and fingerprints (a major category of individualization pattern).

Pattern evidence can be very important in an investigation, because it includes many types of evidence familiar to most people. Some types of patterns can potentially be individualized— that is, attributed to a specific source. In this way people can be associated with or dissociated from specific places, like scenes, or from other people. Conclusions from pattern evidence comparisons are usually more definitive than those from trace or chemical evidence—and correspondingly more useful to juries and judges. Pattern evidence is examined by the eye, for the most part. No complicated instruments, other than the occasional use of microscopes, are required. Sometimes a pattern evidence match can be obvious to anyone, such as in a physical pattern match (jigsaw fit), making the evidence easier to present to a court.

8.1 Classification of Pattern Evidence Pattern evidence can be classified into three overarching categories: patterns for identifica- tion, patterns for individualization, and patterns for reconstruction. This idea follows by anal- ogy from the three activities that can make up the elements of a forensic investigation—iden- tification, individualization, and reconstruction—that we discussed in Chapter 1. So, just as we can talk about identification, individualization, and reconstruction as elements of a crimi- nalistics investigation, so can we talk about pattern evidence categories that have these ele- ments as their goals.

Identification (or classification) patterns, which are used to identify things in our every- day environment by general shape and form, are applied in forensic work to hair compari- sons (Chapter 6) and handwriting (Chapter 9). The different individualization patterns that are important in forensic work are discussed in detail in this and the next chapter. In later chapters, we briefly discuss some reconstruction patterns, including bloodstain patterns. Before specific types of physical patterns are discussed, let’s go over each category of pattern evidence.

Patterns for Identification Patterns for identification are used to identify objects and people in our everyday life and experience. For instance, right now, you might be sitting at a table. How do you know it’s a table? You might say, “I know it’s a table just by looking at it.” The reasoning behind your knowledge is that your brain has a record of the pattern of a table, which you learned when you were younger. This pattern has to do with the shape and form of a table: its four legs and

Section 8.1Classification of Pattern Evidence

flat top. There are variations of tables in the world, but on the basis of their general pattern, we classify them all as tables. When you see this particular pattern, it matches up with the brain pattern that identifies it as a table. This works the same way for facial recognition. You recognize people you know instantly—even in a large crowd and even if you haven’t seen them in a long time. But what if one of your friends tries to describe someone new to you in enough detail for you to find this stranger in a crowded place, like an airport? No matter how much detail is provided, you may not find him or her. It is very difficult to enumerate the fea- tures and properties of a person’s facial pattern that one person recognizes in enough detail to allow someone else to do so.

The human mind is very good at pattern recognition, but it is not yet clear in a detailed way how it works. In forensic work, the examinations that most closely resemble this type of pat- tern are hair comparisons and handwriting comparisons. In comparing hairs or handwriting samples, the examiner looks at specific features in the known and the questioned sample. But the comparison is more than just a checklist of which features match. The examiner incorpo- rates the sum of all these feature comparisons into an overall pattern comparison between the questioned and known. It is a lot like the facial recognition example. Recognizing some- one’s face is more involved than a simple checklist of the features that are compared. One of the important things that distinguish handwriting and hair comparisons from the other evi- dence category comparisons is intraindividual variability, which means that there is variabil- ity in the knowns themselves, and this must be taken into consideration in the comparison. One could argue that handwriting or hair comparisons fall into the individualization pattern category. Similarly, face recognition of a specific person involves an individualization pattern comparison.

Patterns for Individualization Patterns for individualization are characteristic of evidence that can be unique among the members of their class. This can be very important associative evidence in an investigation. We might be able to figure out that a particular tire made a tire mark, that a particular piece of footwear made an impression, or that broken pieces of a headlight lens came from a specific car in a hit-and-run, which may tie a suspect vehicle to the scene of a crime. There are two major types of individualization patterns: physical match patterns and impressions.

Physical Matches Physical match patterns are formed from the pieces of randomly broken objects and are sometimes called “jigsaw fit” matches. The patterns are like a picture puzzle. For instance, if a glass was broken and there weren’t too many pieces, it wouldn’t take long to figure out how the pieces fit back together to form the original glass. Even if some pieces were missing, it would be likely that at least a few pieces would fit together. Note that this works for solid objects that fracture in a random fashion. In cases of solid objects, these physical matches are also known as fracture matches.

Suppose that several pieces of a broken glass were found at a crime scene. Later, a suspect was developed, and police searched his apartment. In the cuff of a pair of pants, a piece of glass was found. The lab performed an analysis and physically matched the pants-cuff piece to the glass pieces from the scene. This evidence goes a long way toward putting the owner of these pants at the scene around the time the glass was broken.

Section 8.1Classification of Pattern Evidence

When the object that fractures is solid and breaks in a random fashion, the physical matching of the pieces is called direct, or sometimes primary. If an object or item isn’t solid or fractures in a way that doesn’t result in clean, smooth fracture surfaces—such as pieces of cut or torn fabric or a snapped piece of wood with ragged irregular ends—the physical match is called indirect, or secondary. Experts can work to try to fit these pieces back together, but even if the match looks right, there is uncertainty. It is much easier to imagine a piece of similar cut or torn fabric “matching” an unknown by chance than it is in the broken glass case. Experts will not generally say that secondary physical matches are true individualizations. Instead, they might say the pieces fit and are consistent with having been part of the same original, but they cannot confirm a common origin.

Impressions Another major type of individualization pattern is impressions. Impressions occur when two objects come in contact with one another and one object leaves behind distinguishing markings on or in the other. There are three types of impres- sions, which are distinguished based on depth and how the marks are made. Impressions that are essentially stamped by an object into or onto another are called imprints if they are more or less flat (two- dimensional). They are called indenta- tions if they have depth (three-dimen- sional character). For example, many fingerprints and tire impressions are imprints because they are left on hard sur- faces. However, they can be indentations if they are left in a soft receiving medium, such as a fingerprint in soft tar or a tire impression in soft soil. If the receiving surface is marked by an object or surface moving across it—in effect, being scratched by it—the marks are called striations. The markings on bullets that firearms examiners use to identify the gun from which a bullet came are striations. Any sliding tool mark, like a mark made by a screwdriver scraping across a latch plate on a door, is also a striation.

Think About It

In the previous example about the suspect and the piece of broken glass, are you convinced that this evidence places the suspect at the scene around the time the glass was broken? What if you were an expert witness and the suspect’s lawyer asked, “How do you know glasses break randomly? Why couldn’t there have been another glass in my client’s kitchen that broke in a way that produced the piece the police found, and it just happened to fit the scene pieces?” How would you answer the lawyer’s question? How would you prove that glass breaks randomly and show that this is really an individualization? Is this something that can be proven?

Alexandre Meneghini/Associated Press Bullet striations leave distinct impressions that can be used to match them to the gun from which they were shot. What are some other examples of striations?

Section 8.2Collection and Preservation of Pattern Evidence

Patterns for Reconstruction Patterns for reconstruction help create theories of the events that occurred at a scene. Recon- struction patterns include glass fractures, furniture and objects at a scene, tracks, trails, tra- jectories of projectiles, skid marks in auto accidents, and more. Fracture patterns in glass can help determine what caused the breakage. The distribution and condition of clothing and objects at scenes can help determine what happened, if there was a struggle, movements of persons involved, and so forth. Tracks and trails can help show the direction of movement of people. Projectile trajectories, such as the path followed by a bullet in a shooting case, can help reconstruct the position of the weapon with respect to the target. Skid marks help auto- mobile accident reconstruction specialists determine the direction and speed of vehicles just prior to an accident. Depending on the speed and direction of a vehicle at the time its brakes are applied, a tire skid mark with a particular length and direction is created. Documenta- tion and measurements of the marks can help reconstruct direction and speed. There are computer programs now that assist traffic accident reconstruction specialists in these tasks.

8.2 Collection and Preservation of Pattern Evidence There are different ways of collecting pattern evidence, depending on the markings or impres- sions left behind. Two important terms to know are positive and negative impressions. A posi- tive impression is identical to the object that made it, whereas a negative impression is its mirror image. The shoe prints left in the mud are negative impressions; they are negatives of the shoes’ soles. In this scenario, the positives would be the shoes’ soles. The same is true in the case of a tire indentation. This mark would be collected by casting. The resulting cast is a positive, like the tire that made the mark, so the cast can be compared to the tire.

In general, imprint markings are collected by first photographing the mark with and without a scale present, and then either collecting the whole object that has the mark, or if that is not possible, by tape-lifting. If the imprint markings are made up of dirt or grease or other resi- dues, they can be lifted from a surface with sticky tape (similar to Scotch® tape). The tape must be placed onto the surface with care, to avoid creating any bubbles. A rubber roller can help in this process. Then the tape is carefully lifted, so as to avoid any damage to or distortion of the mark, and placed onto a contrasting backing surface. A black mark, for example, would be placed onto a white backing surface. This item is then labeled with the usual required information and placed into a paper or plastic container and sealed. Lifting tapes of various sizes and appropriate backings are commercially available.

Indentation markings must also be photographed. As mentioned in Chapter 2, side lighting can help give the impression better contrast. After photography, the mark is cast. For this purpose, dental stone is used. This is a special finely ground plaster used by dentists to make molds for restorations. It is mixed with water to make a pancake-batter-consistency mixture, then poured into the indentation so as not to disturb any of the detail present. Once it hard- ens, it can be removed. It captures fine detail quite well. In addition to labeling the packaging of a cast, the collector can scratch a case number or item number into the top side of the hard- ening dental stone. There are special types of casting materials for tool marks, marks in snow, and other specific types of marks. Tool marks are discussed in a later chapter, but for now, dental stone is not capable of capturing the very fine detail in a tool mark (like a striation

Section 8.3Analysis of Pattern Evidence

mark made by a screwdriver on a lock plate). There are silicone-based materials commercially available that are better suited for this task. These silicone-based materials can also be used for indentation-type fingerprints, such as a fin- gerprint in wax. Indentation markings in snow pose a problem because dental stone gives off heat as it hardens, and the heat can melt the snow and destroy the impression detail. Prod- ucts like Snow Print Wax can be sprayed onto the mark to protect it from this effect. An indenta- tion impression is a negative, and so the cast of the impression is a positive. Accordingly, the cast can be compared directly with the tire or foot- wear or other item that is thought to have made the indentation.

Both in collecting evidence and in thinking about how pattern comparisons are done, it is impor- tant to remember that comparisons must be made between like impressions—left with left, right with right, positive with positive, and nega- tive with negative. The detailed individual char- acteristics that help in individualizing the mark must be in the same orientation as the original object that made the mark (or as its mirror image). Sometimes this requires that the lab cre- ate a known from the suspected item in order to make the comparison. For example, a lifted foot- wear impression from a scene would be com- pared with an inked impression of the suspected footwear made in the laboratory.

8.3 Analysis of Pattern Evidence In Chapter 1.4 class and individual characteristics were introduced. These concepts become very important in physical pattern analysis. Consider items like shoes or tires. There are hun- dreds, or maybe even thousands, of basically identical shoes and tires in the world. They were manufactured under quality control standards to be as similar as possible. So if a brand-new

Johner/SuperStock Snow prints are among the most difficult indentation markings to collect and preserve. Can you think of any other environments where pattern evidence would be particularly hard to obtain?

Think About It

Imagine you are a pattern evidence examiner, and the police bring you a tape-lifted impression of a tire they have gotten from a flat concrete surface. They have a suspect car, but it is up to you to figure out how to compare the tires with the impressions. How would you make the known specimens from the tires to use for comparison with the questioned impression?

Section 8.3Analysis of Pattern Evidence

shoe or tire leaves an impression, what characteristics make up that impression? Class char- acteristics. With a new shoe, the sole pattern, manufacturer, size, type of shoe, and so forth, can be determined. However, it is impossible to distinguish any individual shoe in that class, because there are not yet any individual characteristics. The same rule applies to tires. Indi- vidual characteristics come about as a result of wear. Sole or tire pattern features wear down in nonuniform ways, parts of the sole or tire can be cut or torn by wear, foreign objects can make unusual marks in the sole or tire material, and so on.

The forensic examiner will make a comparison between a questioned mark and a known object. If you recall, questioned objects are found at the scene and have an unknown source. Known objects have a known source and can help determine the source of a questioned object. Here, the matter of questioned and known specimens becomes a little more complicated with the inclusion of positive or negative impressions. A sneaker sole itself, for instance, cannot be compared with the impression mark because positives and negatives cannot be compared directly. The features of interest would be mirror imaged. Take a good look at Figure 8.1.

Figure 8.1: Sneaker sole impressions

Analysis of pattern evidence, such as this sneaker sole, requires that the correct type of impression (positive or negative) and orientation be used to make a comparison between the unknown and the known mark.

Adapted from Spantomoda/iStock/Thinkstock

(a) Image of sole (b) Ink impression on transparent plastic

Section 8.3Analysis of Pattern Evidence

The figure shows a left sneaker, but it is a mirror image with respect to the inked impression on the brown paper. To make a comparison, the sneaker must be used to make a known nega- tive impression. This might be an inked impression on paper or on transparent plastic. These are good surfaces for capturing the detail in the footwear in approximately the same way as it was captured in the evidence mark. Note that these inked impressions would be made by someone actually wearing the sneaker and taking a step, so that there would be weight on the shoe. The middle impression on transparent plastic in Figure 8.1 is turned to match the orientation of the sneaker in the picture, but if it is turned over, it will match the orientation of the paper print. As an inked sneaker impression, it is a negative and therefore could be used as the known for an unknown imprint thought to have been made by that sneaker. You can also see from Figure 8.1 how it would be easy to confuse left and right if you don’t keep track of what you are doing when making these impressions on transparent surfaces.

Physical Matches There are four criteria that must be met in order to state that evidence is individualized in a fracture match. The criteria include the following.

1. The objects must be broken, torn, or cut. 2. They must be capable of being realigned. 3. There must be a jigsaw fit (or lock-and-key fit) surface to surface. 4. The match must be unique.

With indirect or secondary matches, such as torn fabrics, it is unlikely that individuality can be declared, even if the pieces appear to fit. It isn’t intuitive that every fabric cut or tear will be completely random and thus unique. This means that there is a possibility of a chance dupli- cate. Two different cuts, or even tears, of a fabric could be so similar as to be indistinguishable in a comparison.

Physical matching is done by the eye or with the aid of a magnifier or stereo microscope. This is a microscope with two eyepieces (enabling stereo vision) that is essentially a magnifier. This type of matching is intuitive and quite familiar to people. As a result, it is very convincing for a jury or judge, because they can look at it and see it for themselves. This can be danger- ous, however, because if an expert overinterprets a match, there is a better chance the jury will believe him or her.

Impressions With the other impressions that have been discussed, such as those from shoes or tires, the comparison is more subjective and will depend on the examiner’s training and experience. These comparisons are also done by the eye or with the aid of simple magnifiers. The indi- vidual characteristics must be located and their position within the overall pattern noted. With experience, examiners develop a sense of what the different individual characteristics are in each impression. They also learn to judge the quality of the impression and how many individual characteristics it possesses. As you can imagine, not every impression gives good detail. It might be light, smudged, or distorted. Examiners use these factors to determine if known and unknown markings match. There is no rule about how many matching individual characteristics must be present to declare that the known is the source of the questioned. This determination is up to the examiner and is thus more subjective. Unlike a physical match,

Section 8.3Analysis of Pattern Evidence

these comparisons are not intuitive or obvious, and the skill to do them comes only from extensive training and experience.

As with the random fracturing of solid objects, individuality due to wear comes about because the accidentals, the individual characteristics acquired by the item, are expected to be ran- dom. With a sneaker sole, for example, this might be a cut or a particularly worn area. An examiner must use his or her training and judgment to assess the quality of the impression and the number and distribution of individual characteristics that were transferred to the mark from the object. These factors help the examiner decide what conclusion to draw from the comparison.

Other patterns can fall into this general category. Occasionally, a lip print or ear print is exam- ined. These imprints are unusual, so there is not much examiner experience with or research on them. Thus, there is not much of a basis for finding enough individual characteristics to reach an unambiguous conclusion. Sock prints or glove prints may be included here, as well as fabric impressions, such as when a blood-soaked fabric is pressed against a nonabsorbent surface and leaves an impression in blood. Sometimes, in a hit-and-run case, the pattern of the fabric from the clothing of a victim can be impressed into the bumper of a vehicle.

Bite marks can be included here, as well. Only forensic odontologists deal with bite mark comparisons, but these marks can be considered members of the patterns for individualiza- tion category. Bite marks are complicated because different numbers of teeth might make them, they are frequently on curved surfaces that can change or shrink, and it is difficult to prepare truly proper knowns for comparison from a suspect’s teeth. One can make models (casts) of someone’s teeth, but it is not easy to reproduce the evidentiary mark, because they are usually on living skin and the surfaces are often curved. Up until around 10 years ago, forensic dentists sometimes declared that a bite mark could be individualized and could iden- tify a particular person. There were a number of cases in which bite mark evi- dence figured in a criminal conviction.

One famous example of these cases occurred in the Florida trial of the serial murderer Ted Bundy. Bundy was one of the most prolific serial murderers in U.S. history. He is known to have killed dozens of women in Washington, Oregon, Idaho, Utah, Colorado, and Florida, and investi- gators familiar with him think there were many others. His entire story is long and complicated, but the bite mark evidence against him came in the murder of two Chi Omega sorority sisters and the assault on two others in their sorority house at Flor- ida State University in January 1978.

Two forensic odontologists testified that the bite marks on the murdered women were from Bundy. Bundy was executed on January 24, 1989. Leading up to his execution, he talked to investigators from several of the western states where he had lived; he confessed to a long

Associated Press Bite mark evidence is not as accepted today as it was during Ted Bundy’s trial. Do you think the case’s outcome might have been different if bite marks were considered circumstantial evidence?

Section 8.3Analysis of Pattern Evidence

list of murders, some of which the police hadn’t even known about. He was such a skilled liar, however, that police could never be sure how many victims there really were.

However, recently, the tide has turned against bite mark evidence. A 2009 report by the Com- mittee on Identifying the Needs of the Forensic Sciences Community was highly critical of the discipline, finding that “the scientific basis is insufficient to conclude that bite mark compari- sons can result in a conclusive match” (p. 175). An investigation by the Washington Post published in 2015 came to the same conclusion, bringing forward two cases in which people were accused of murder based on bite mark evidence (Balko, 2015). In these cases, later DNA typing of saliva around the bite mark on the victim showed that the saliva did not match the person whom the forensic odontologist had positively identified. Also in 2015, the White House Office of Science and Technology Policy called for bite-mark analysis to be abandoned, as it did not have a strong scientific basis (Augenstein, 2015). Due to this accumulation of evidence, bite marks are not generally attributed to a specific person anymore. It is more likely that a dentist will say either that the person is excluded or could not be excluded.

Individualization The term individualization has been used frequently in this discussion. The term means uniqueness—the only one, to the exclusion of all others. Recently, there has been discussion among pattern analysts about whether uniqueness is a realistic conclusion based on their knowledge of and experience with many of these patterns. How is anyone sure there is no chance duplicate anywhere? There has been a trend in the direction of changing the termi- nology to describe persuasive matches as a single source (Polski et al., 2011). If a phrase like attributable to a single source were to be used and defined in an understandable way that sug- gested a strong possibility of individuality or common origin but permitted some uncertainty, it could be a better reflection of the state of knowledge. Experiments on pattern matching will continue, but in truth there is no way to compare any given pattern with every possible source. Even if a single pattern were studied—for example, a striation tool mark made by a screwdriver on a scratchable surface—it is nearly impossible to replicate. The angle, the pres- sure, the speed of movement—these could all affect the appearance of the final mark. And that is only in one surface! So we have to rely on the scientific concept of induction. If we have good information on basic principles about a representative number of possible situations, we can, by inductive logic, extend them to cover all the marks in that category.

Think About It

Bite marks are no longer considered a way to specifically identify someone, but they can be used to exclude or include a person of interest. Do you think that if Ted Bundy were on trial today, the bite marks would still be a key piece of evidence against him? If you were the odontologist testifying in the trial, how would you explain the bite marks to the court? What language would you use to indicate that you thought he was probably the biter but that there wasn’t any scientific way to really establish that fact?

Section 8.4Fingerprints

8.4 Fingerprints Among the oldest and best established individualizing markings, fingerprints remain one of the most important types of physical evidence in the repertoire. A fingerprint impression from a scene matched to the known fingerprint of a suspect essentially proves that the person was there at some point. Almost everyone believes that fingerprints are highly individual. It has become part of our unspoken culture. People talk about “DNA fingerprinting” and use the term unique to describe a fingerprint.

Fingerprints are a form of biometric identifier, a biological measurement or feature of a per- son that has the potential of being used as the basis for individualization. Other types of bio- metric identifiers include DNA; facial features; parts of the eye, such as retinas and irises; and even handwriting.

There is interest in biometrics as individuality markers because they are difficult to repro- duce or forge. All documentary identification systems have been subject to forgery, including driver’s licenses, passports, credit and debit cards, and employee identifying cards or badges, making it possible for a criminal to change his or her identity. This is more difficult and less common with biometric markers.

Fingerprints are an attractive biometric because they are formed during a person’s develop- ment in the womb, are permanent and unchanging throughout life, are easy to record and scan unobtrusively, and involve a bare minimum of privacy invasion to record. Something to remember about the use of fingerprints as biometric identification vehicles is that the goal is not to individualize the person among everyone in the world. That is not necessary. A system might be put in place to distinguish employees who work in a large, secure defense plant or every airline passenger who is a frequent flyer with United Airlines. It is possible to determine how many features an automated scanning system has to distinguish on how many different fingers to tell apart some specific number of people. The theory behind this technology is, of course, the basis for automated fingerprint identification systems. And it is important in get- ting at the question of fingerprint individuality, because it represents an automated method for comparing large numbers of prints for individual characteristics.

Nature of Fingerprints The beginning of the recognition of fingerprints as a unique personal identifier is shrouded in the mists of history. Fingerprints are the result of a type of skin called friction ridge skin, which is found on the ends of the fingers, in the palms, and on the soles of the feet of primates, including humans. Though palm prints and footprints can be compared and analyzed, the most work has been done on fingerprints.

As shown in Figure 8.2, there are three basic fingerprint patterns: arches, loops, and whorls.

Section 8.4Fingerprints

Figure 8.2: Three basic fingerprint patterns

Can you see the differences between the fingerprint patterns? Which patterns are on your fingers?

Adapted from andregro4ka/iStock/Thinkstock

An important development in the history of fingerprints was classification systems. Classi- fication schemes are based on all 10 prints from an individual. The basic pattern is deter- mined from each print, and within the basic patterns, fingerprints have certain ridge features that they all share. Fingerprint examiners call these features minutiae (singular: minutia), and three of them are important to fingerprint examiners when they compare prints. These are the dot, the bifurcation, and the ridge ending (see Figure 8.3). Note that these minutiae can be present in more than one place in the print pattern and that the location varies from print to print. The type, number, and location of minutiae within a print form the basis of its individuality.

Figure 8.3: Key minutia features

Now that you know the fingerprint patterns on your fingers, examine them again. Can you find examples of the key minutiae features? (It is easier if you make a fingerprint to look at).

Adapted from ponsuwan/iStock/Thinkstock

Arch Loop Whorl

Ridge ending Dot

Bifurcation

Section 8.4Fingerprints

History of Fingerprints for Identification There are indications from archaeological excavations that the use of fingerprint and hand- print patterns as methods of personal identification dates back thousands of years (Berry & Stoney, 2001). They are thought to have been used as signatures and marks of authenticity.

The study and use of fingerprints as unique identifiers can be traced to the 17th and 18th centuries in Europe. The English plant morphologist Nehemiah Grew (1641–1712) published very accurate drawings and descriptions of ridge patterns in a paper called “The Description and Use of the Pores in the Skin of the Hands and Feet,” published in the Philosophical Trans- actions of the Royal Society of London (1684). Then Johannes Evangelista Purkinje (1787– 1869), a Czech physiologist, wrote about friction ridge patterns and described a number of fingerprint patterns in his thesis in 1823. Thomas Bewick (1753–1828) was primarily known as a wood engraver whose engravings appeared in books. He appears to have “signed” his work with his own thumbprint, believing it to be as unique as his signature.

British civil servants in India, beginning around 1850, were important contributors to the development of fingerprints as a means of personal identification. One such person, Sir Wil- liam Herschel, is often credited with being the first European to recognize the value of finger- prints as a means of identifying individuals. Dr. Henry Faulds, a Scottish physician, is known to have been involved in the study of fingerprints by at least 1879. Faulds noted that finger- prints could be classified and that ridge detail appeared to be unique, and he mentioned the idea of apprehending criminals by locating fingerprints at scenes. He wrote to Charles Dar- win (the scientist responsible for proposing the theory of evolution) about fingerprints, who then forwarded the letter to Francis Galton. Galton, a well-known scientist and early genetics researcher, has been said to have put the study of fingerprints on scientific footing. Galton became interested in the subject of fingerprints and put much thought into figuring out how to show that fingerprints were individual. Fingerprint minutiae are sometimes called Galton features in recognition of his contributions. Thomas Taylor, a U.S. Department of Agriculture microscopist, noted in a scientific journal article in 1877 that fingerprints and palm prints might be used as identification features, especially in criminal matters.

To understand and appreciate how fingerprints came into widespread use, some background on a technique called anthropometry is necessary. Anthropometry involves the measurement of the human body and its parts and can be regarded as the first recognized biometric iden- tification method. This method was created by Alphonse Bertillon (1853–1914) and laid the foundation for the eventual acceptance of a biometric parameter as an objective basis for personal identification in a law enforcement context. Bertillon came up with this concept while working with the Paris Police Prefecture, where his duties included filling out and fil- ing criminal information cards. The criminals were skilled at avoiding identification by using

Think About It

Compare the patterns and minutiae of your fingerprints with friends or family members. Do you see the differences? Do you think fingerprints are an accurate and reliable way to identify people?

Section 8.4Fingerprints

disguises and aliases. It occurred to Bertillon that individual physical features could be used to uniquely identify people on criminal records, and he developed a system of measurements that included head size, finger length, and so forth, ultimately choosing 11 different measure- ments. The information was recorded on file cards, and a system was devised for organizing the files. His superiors doubted the system, but it soon proved its value by enabling the police to identify repeat arrestees even if they provided alias names. Bertillon eventually became director of the identification bureau of the Paris Police. Police agencies in many other places began to use his system—often called Bertillonage. Its ultimate undoing was the unequivocal proof that different individuals could have the same anthropometric measurements.

A well-known example of this chance duplication came at the US federal prison at Leaven- worth, Kansas. A new prisoner named Will West was having his measurements taken when a staff member began to suspect that he had encountered this profile before. Upon investiga- tion, he found that the same measurements fit a man named William West who was already incarcerated at the prison (and unrelated to Will West, although they looked a lot alike). How- ever, the two did have different fingerprints. This incident, and others like it, eventually con- vinced police identification specialists that fingerprints represented the basis for a superior method of personal identification.

Around 1893 the British Home Office, parent agency of the London Metropolitan Police (Scot- land Yard), decided to add fingerprints to the Bertillon cards for criminals in its identification system. Before long, the success of fingerprints overshadowed that of Bertillonage in criminal identification, and anthropometry was abandoned in 1901.

Sir Edward Henry (1850–1931) was a member of the British Indian Civil Service, beginning in about 1873. In 1891 he became inspector general of police for Bengal province, where anthropometry was in use for criminal identification. He became interested in fingerprints, read Galton’s book, and corresponded with and later visited him. Galton shared all the infor- mation he had about fingerprints with Henry, including materials he had obtained from Her- schel and Faulds. Henry is widely known for working out a fingerprint classification system that was adopted in British India and presented to people in the United Kingdom in 1899. He wrote a classic book entitled Classification and Uses of Fingerprints.

Juan Vucetich (1858–1925) was the western hemisphere’s fingerprint pioneer. An employee of the police department in La Plata, Argentina, he became convinced of the value of finger- prints as a means of criminal identification and wrote a book on the subject in 1894.

By 1896 the Argentine police had abandoned Bertillonage in favor of fingerprints in criminal records. The first recorded case in which fingerprints were used to solve a crime took place in Argentina in 1892. A woman named Francisca Rojas alleged that her two children were murdered by a man named Velasquez. Investigators examined her home and found a bloody thumbprint on the bedroom door. Vucetich compared the fingerprints of Rojas and Velasquez to the bloody fingerprint and that found it belonged to Rojas, linking her to the murder of her children. Vucetich devised a classification system for fingerprints that was used in Argentina and throughout South America.

In North America, fingerprints were in use by the New York City civil service (to prevent impersonations during examinations) by 1903, and fingerprints were introduced about the same time in the New York State prison system and at Leavenworth. A number of police

Section 8.4Fingerprints

departments began using fingerprints as identifiers in criminal records as well. The 1904 St. Louis World’s Fair provided the venue for a chance meeting between Inspector Edward Foster of the Royal Canadian Mounted Police (RCMP) and Detective John Ferrier of Scotland Yard. As a result of what he learned in St. Louis, Foster convinced his superiors in the RCMP of the utility of fingerprints. In 1910 a man called Thomas Jennings was arrested in Chicago and brought to trial for murder. The primary evidence against him was fingerprints. The state, which wanted to ensure that the fingerprint identification evidence would survive the anticipated appeal to the Illinois Supreme Court, called Edward Foster as an expert witness. The defendant was convicted, the evidence did survive, and the Jennings case is considered a landmark fingerprint case in criminal jurisprudence.

Fingerprint Identification Organizations Now that fingerprints have become a major biometric indicator and play an important role in criminal investigations, there are a couple of important organizations that fingerprint exam- iners may choose to become a part of. The International Association for Identification (IAI) is the primary professional organization for fingerprint examiners. It has extensive certification programs, and its latent print certification is difficult to obtain. Many physical pattern com- parison specialists also belong to the IAI.

Another important group is the NIST OSAC Friction Ridge Subcommittee (FRS). This com- mittee is a consensus standard–setting body for all comparisons involving friction ridge skin (fingerprints, footprints, palm prints). This group supplanted the Scientific Working Group on Friction Ridge Analysis, Study and Technology, which was the previous standard-setting body for this specialty.

Fingerprint Classification and File Storage When all fingerprint records consisted of inked impressions on a 10-print card, a classifica- tion system was very important. How else could the cards be filed so that they were easily found? Classification was based on a 10-print card, not on a single print. You needed all 10 prints from a person to classify the prints.

In most criminal cases in which fingerprints are recovered, there is only one—or sometimes only a partial—impression of one finger. In such a case, how would authorities locate it in their card file? Simply put, they couldn’t, which was the problem. Sometimes there might be one or more suspects, and their fingerprints could be pulled for comparison. But if there weren’t any suspects, there was no realistic way to search drawers that were full of files to look for one fingerprint. That is why the advent of the Automated Fingerprint Identification System (AFIS) revolutionized the use of fingerprints.

The system consists of a scanner that records images of all 10 prints and stores them on a server. It includes many workstations from which operators can enter new fingerprints and search the system for existing ones. The way in which the system works is relatively simple. The examiner begins by scanning a fingerprint, and computerized algorithms mark the minu- tiae to search for. The computer then calculates a score based on the degree of match. Most of the time, the matching print will appear in the first few entries, if it is in the system. The exam- iner must pull up the likely matches and visually compare them with the fingerprint in

Section 8.5Collection and Preservation of Fingerprints

question. The computer is not used for matching prints for court purposes. That is something only an examiner can do. AFIS is used to provide possible matches, helping narrow down the list of individuals the fingerprint could belong to. An examiner will then need to compare the fingerprint and the possible matches provided to make the final decision on the identification of the fingerprint.

8.5 Collection and Preservation of Fingerprints There are two topics that must be considered in terms of collecting and preserving finger- prints for a case. The first is collecting or taking fingerprints from known individuals. The second is collecting fingerprints from crime scenes and objects.

Collection and Preservation of Knowns At one time, fingerprints were taken from known individuals by inking the fingers and impressing them onto fingerprint cards (as seen in the cover photo for this chapter). In addi- tion to including a labeled box for each finger, there was space on the bottom of the card to reprint the thumbs and to impress the four fingers of each hand. These impressions served as backups if the main boxed impressions were not of high enough quality for a comparison. Fingerprints from these 10-print cards can be scanned into AFIS systems to build the single- print databases.

Today most fingerprints are collected by Live Scan technology. The person places each fin- ger (and thumb) onto a small scanning plate. Sometimes there is an on-screen guide to help the person adjust the position and pressure of each finger. The device then scans the prints directly into an AFIS. These devices can be seen at ports of entry into the United States, such as in international airports.

Fingerprints are also preserved electronically. The largest database of fingerprints is con- tained in the FBI’s Integrated AFIS (IAFIS) system. The system contains over 70 million print files from criminal histories and about 35 million other files. People who are arrested are fin- gerprinted. But many other people may be fingerprinted as well, like those who have firearms permits or security clearances or have undergone background checks for a variety of reasons.

Collection, Preservation, and Processing of Evidentiary Prints Collecting fingerprints from scenes is similar to collecting evidence from a scene, but it is more complicated than collecting known prints. Sometimes prints at scenes are visible, but often they are not. The ones that are not require some sort of development or processing to

Think About It

Do you think that 10-print cards and/or AFIS systems are a good way to organize and store fingerprint data? What other ways can you think of that could improve the filing system?

Section 8.5Collection and Preservation of Fingerprints

render them visible. The first decision an investigator must make is whether to use devel- opment (visualization) techniques for prints at the scene or to bring the object bearing the print back to the lab. The larger and more unmovable the object or surface, the more likely an investigator would be to employ development techniques in the field. After locating and/ or developing the print or prints, the crime scene processor must either collect the whole object the print resides on or collect the fingerprint alone. Photography and sketches are used to document the location of the fingerprint or the object containing it at the scene. The print or developed print must also be photographed. It is best if the photo can be 1:1 (life-size image). That way there is no compression of the details. If a print has required development, it may be possible to tape-lift the print, depending on the type of development. All the usual rules about chain of custody pertain here. The item bearing the print or the tape-lift must be carefully packaged, labeled, and sealed. Items have to be packaged so as to provide maximum protection of an undeveloped print impression. Nothing should touch or rub the impression during storage or transport. Some type of wood or plastic trough must be used to protect the ridge impressions from the package during transport. Developed latent prints must also be protected. Tape-lifts are placed onto backings and are thus protected.

There are three kinds of fingerprint impressions encountered: visible, plastic, and latent.

Visible Fingerprints Visible prints are also sometimes called patent. Visible prints are made in dirt, ink, blood, or some other medium that is visible to the eye. These would be photographed and, if possible, the object on which they are deposited would be collected.

Plastic Fingerprints Plastic prints are three-dimensional and are made in soft receiving materials like silly putty or tar. These are indentation prints. They are first photographed. Then the object bearing the print is collected, if possible. If not, this type of fingerprint impression can be cast in the same manner as footwear indentations, only the casting materials are silicone-based and capable of capturing fine detail much better than any type of plaster.

Latent Fingerprints Latent (hidden) fingerprints cannot be clearly seen or visualized without some development or processing. There are three basic methods of processing or developing latent fingerprints: physical, chemical, and instrumental. The most common and familiar physical method is pow- der dusting. Here a fingerprint powder (usually black) is applied with a fine brush to the

Think About It

What do the techniques and procedures for evidentiary fingerprint collection and preser- vation have in common with the collection and preservation techniques for other pattern evidence? What are the differences?

Section 8.5Collection and Preservation of Fingerprints

latent print residue. The powder particles adhere to the fatty components in the residue and make the ridges visible. Another technique used is called magna brush. Here a small magnet is used to apply magnetic particles to the print residue. These particles adhere to the latent residue the same way as the powder particles. Powder-dusted (including magna-powder- dusted) prints can generally be lifted using transparent tape. The tape must be placed care- fully onto the dusted print to avoid any air bubbles. This can be done with a rubber roller. The tape is lifted all in one slow motion, and the transparent tape-lift is then placed onto a contrasting background, such as a white surface. Another, more complex technique uses molybdenum disulfide particles in a solution. This is known as small particle reagent and works on surfaces that are wet. Lifting of a print developed via small particle reagent can be accomplished without letting the surface dry if the tape is carefully applied to the center and pressure applied in all directions outward, pushing away the liquid droplets in the process. Latents on wet surfaces aren’t common, but the situation does arise. Think of a can of beer with a latent on it, taken from the refrigerator and allowed to sit out for a while in a humid environment where water can condense onto the can.

The classical chemical techniques for print development were silver nitrate, iodine fuming, ninhydrin, and superglue. Silver nitrate development works on the same principle as the development of pho- tographic film, in which silver chloride is chemically reduced to metallic silver. Iodine fuming is based on iodine mole- cules going from solid to vapor without becoming liquid (a process called subli- mation). The iodine vapor can interact with fingerprint residue and give it a tem- porary color. The color can be made per- manent with other chemicals. Neither sil- ver nitrate nor iodine are used for latent prints anymore, because the other tech- niques are better or equivalent. Silver has gotten expensive, and it creates a disposal problem after use. Other techniques are better than iodine because they have the potential for greater sensitivity.

Today ninhydrin or superglue treatment is followed by an additional treatment with other chemicals to make the visualization more sensitive—that is, lesser amounts of residue can be detected. Ninhydrin is a chemical that reacts with the amino acids in fingerprint residue. Amino acids are the building blocks of proteins. Superglue can be fumed onto fingerprint residue, where it reacts to form a semisolid, whitish deposit on the ridge patterns. Superglue will vaporize by itself, and the process can be accelerated with heat. The vapors, or fumes, interact with the fingerprint residue. The superglued fingerprint is fairly permanent, but it can be powder dusted and the dusted print lifted. This is done in the same way as lifting dusted fingerprints, as described earlier. Superglued prints can also be further treated with other chemicals by dipping or spraying to make the visualization more sensitive. Ninhydrin is the method of choice for absorbent surfaces like paper or Sheetrock. Superglue will work on practically any surface.

Franz12/iStock/Thinkstock Fingerprints at the scene of a crime are often latent and are found after an investigator has dusted or used another method to look for them.

Section 8.6Analysis of Fingerprints

The most common instrumental technique is called laser illumination. With this process, fin- gerprints are commonly developed with superglue, on which a chemical called laser dye is applied. When a laser is shined on a fingerprint processed in this way, a very small amount of residue can be visualized and then photographed. Sometimes laser illumination is used directly on fingerprint residues, but this technique is used less frequently. Laser procedures are usually performed in the lab. Portable lasers do exist, but these techniques are very cum- bersome in the field. Laser-illuminated prints would typically be photographed for compari- son. The laser dye procedure is indicated if the ridge patterns are not clear enough for a com- parison following superglue development alone.

Fingerprints in blood can be a special case. Sometimes they are plainly visible (in these cases these would be considered visible prints), but at other times they may require special enhancement techniques. The enhancement procedures make use of chemicals that produce color in the presence of blood. They also contain a sticky substance to make them adhere to the residue and a rapidly evaporating solvent so that bloody prints on a vertical surface don’t run when the chemical is sprayed. These enhancement techniques have the potential of inter- fering with DNA profiling of the blood because the chemicals in the enhancement mixture can adversely affect DNA. It is important for investigators to consider the value of DNA profiling and fingerprint identification to the case in these situations. A small specimen of blood could be collected, for example, without disturbing the ridge patterns a fingerprint examiner would need.

8.6 Analysis of Fingerprints For forensic and legal purposes, fingerprint analysis or comparisons are the heart of the mat- ter. The comparison of a questioned print with a known, and the ability to form an unequivo- cal conclusion, make fingerprints valuable as evidence.

Trained examiners complete the comparisons. The training is lengthy. It can take up to 2 years before a new examiner is allowed to operate without supervision. There is a specific proto- col to be completed for each comparison. The first thing to be decided is whether the print is suitable for comparison. This decision is based on the clarity of the ridges and the exam- iner’s judgment that a proper comparison can be completed. For example, the examiner must determine if there is enough of the print present in the impression and if there are enough visible details (minutiae). The examiner must also determine if the print is easily viewed, is not smudged, and does not have too many impressions overlaid on one another. If the print is judged to be unsuitable for comparison, the examination ends. If the print is judged to be suitable, the questioned print must be properly oriented for comparison with a known (a

Think About It

If you had to choose a single method for processing latent prints in the laboratory, which one would you choose and why? Is choosing a single method appropriate?

Section 8.6Analysis of Fingerprints

whole fingerprint). To perform an accurate examination, the print cannot be upside down or rotated 90 degrees. Next it goes through analysis, comparison, evaluation, and verifica- tion (ACE-V). Analysis consists of judging suitability, arranging correct orientation, and judg- ing the minutiae content of the print. The comparison part is carefully figuring out if every minutia feature in the questioned impression is also in the known—and in the same location. The evaluation step is based on the examiner’s knowledge of and experience with print com- parisons. How common or rare is this pattern? If the examiner is satisfied that there is enough detail and are no unexplained differences between the questioned and known, an identifica- tion can be made. In the verification step, another examiner is asked to look at the prints and verify the first examiner’s conclusion.

As shown in Table 8.1, the main category to which the fingerprint belongs (arch, loop, or whorl) is sometimes called first level, or level 1. The minutiae present and their location are sometimes called second level, or level 2. There is a level 3 as well, consisting of pores and ridge features. Level 3 is not always used, because the first two levels are nearly always suf- ficient for making an identification or determining an exclusion.

Table 8.1: Fingerprint pattern levels

Level Pattern category

1 Arch, loop, or whorl

2 Minutiae (such as dot, bifurcation, and ridge ending)

3 Pore and ridge features

An examiner may reach three possible conclusions following a comparison: exclusion, incon- clusive, or identification. Exclusion means that the questioned print does not match the known print, and therefore the person to which the known print belongs is excluded. Inconclusive means the examiner can neither make the identification nor exclude the person. There isn’t enough information in the questioned print. Identification means that this questioned print is attributable to the person who furnished the known.

In recent years there have been questions as to whether there is a sufficient scientific underpin- ning to fingerprint comparisons to warrant the identification conclusion (National Research Council, 2009; Koehler & Saks, 2010). How do we know fingerprints are individual? The stan- dard answer is that hundreds of thousands of prints have been compared, and no two have been found that are alike. This standard answer is correct in a sense, but one person did not analyze all of these pairwise comparisons. That is, the sum total of all the pairwise compari- sons was done by many different people at different times. Furthermore, an examiner doesn’t compare a questioned print with millions of knowns; the questioned print is compared with only a few. With AFIS systems, the multiple pairwise comparison argument is much more supportable. If a questioned print is searched within IAFIS and found, that questioned print was compared with all the prints in the database. To date, no one has found two or three matches—only one (or none, if the print isn’t in IAFIS). The fact that so many searches have been completed lends considerable support to the individuality idea, but you can make the valid argument that a duplicate has not been found simply because it was not in the system.

Section 8.6Analysis of Fingerprints

Nevertheless, a high-profile case from 2004 has caused some of the thinking to be reconsid- ered. The real question is not so much whether complete fingerprints are duplicated to the extent that a trained examiner can’t tell them apart, but whether there is a chance to get a partial duplicate. That is, presented with an incomplete questioned impression, could there be two prints out in the world that could be interpreted to “match”? See what you think after reading the case of Brandon Mayfield v. United States.

Think About It

From everything you have learned so far, do you think there are two people who have exactly the same 10 fingerprints? What about two people who have one fingerprint identi- cal to one of the other person’s? What about two people who have a partial of one finger- print identical to the partial fingerprint of the other person?

Case Illustration: Brandon Mayfield v. United States Brandon Mayfield was a Muslim attorney practicing in Oregon. He was a U.S. citizen and army veteran. He converted to Islam after meeting and marrying his Egyptian-born wife. On March 11, 2004, a series of coordinated bombings did extensive damage to Spain’s com- muter train system in Madrid, killing 191 people and wounding around 1,800 others. The attack was perpetrated by a local terrorist cell, inspired by but not directly connected to al Qaeda. In the subsequent investigation, a bag containing detonating devices was recovered by the Spanish police, and latent fingerprints were found. These were shared with other countries’ law enforcement agencies to help with the case.

The FBI fingerprint unit ran an AFIS search and generated a number of potential matches. Mayfield’s prints were among them. Possibly because he was Muslim and had provided legal assistance to some Muslim clients, he became a principal suspect. FBI fingerprint experts working on the case came to the conclusion that the evidentiary latents matched Mayfield, and several of them—all highly experienced and seasoned examiners—agreed on this con- clusion. The FBI conducted a detailed inves- tigation of Mayfield and eventually arrested him. There were discussions and at least one meeting between FBI examiners and Spanish fingerprint examiners, in which the latter told the FBI that the prints did not match Mayfield. However, the FBI continued the investigation until it became clear that the FBI was incorrect on this identification. It was found that the prints belonged to an Algerian national named Ouhnane Daoud.

(continued on next page)

Don Ryan/Associated Press Brandon Mayfield at a press conference.

Section 8.6Analysis of Fingerprints

It has been suggested by fingerprint critics that misidentification occurred in this case because of examiner bias. They state that FBI experts knew all about the case and thought it should be a match and that this knowledge ended up deeply prejudicing them. In any event, it does show that identification errors can happen.

You may be thinking as you read this section and this case example, why isn’t there a minimum number of points to define a match? It sounds easy, but it isn’t. There was such a criterion in the United Kingdom for quite some time. But it turned out that nonmatching fingerprints could have the minimum required number of points. It is also the case that an examiner may not always have the minimum number but is convinced the prints match. For these reasons, the IAI, the professional organization that makes international consensus statements about these matters, has long taken the position that there should not be a specified number of matching minutiae or points to declare a match. As noted, the IAI is continuing to examine its principles regarding fingerprint identification (Polski et al., 2011). For a review of the finger- print individuality subject after the NAS report, see the Eldridge article in the Web Resources section at the end of the chapter.

Another way of looking at examiner accuracy is through proficiency tests. Examiners are subjected to these proficiency tests for certification and recertification. Some agencies and accredited forensic labs also participate in proficiency testing for their examiners. At times the tests can be done for research purposes as well. In proficiency tests, examiners are given sets of questioned prints or partials along with known prints and told to complete pairwise comparisons and form conclusions. The vast majority of tests and studies of this type show that the examiners get the right answers. One study involving the fingerprints of identical twins resulted in a few misidentifications (Grieve, 1996). Identical twin fingerprints are dis- tinguishable, but they can be very similar.

Analysis of Other Friction Ridge Impressions Friction ridge skin impressions, such as palm prints and footprints, are compared in the same way as fingerprints are compared. To clarify, oftentimes people refer to “footwear impressions” as footprints, but this is incorrect. Footprints are made by bare feet. The main

Case Illustration: Brandon Mayfield v. United States (continued) The FBI released and apologized to Mayfield, and the government settled a suit he filed against it for $2 million. There was a public discussion involving federal overreach in the investigation, aside from the fingerprint issue. Mayfield sued the government, seeking to overturn parts of the Patriot Act (Lichtblau, 2006). Some sections of the act were initially overturned in lower courts, but federal appellate courts reversed this action upon govern- ment appeal in 2009 (Denson, 2009).

Reflect On It What do you think about the misidentification of this case? Was it bias, incorrect examination of the fingerprints, or a combination of both that led to the wrong arrest? What do you think could have prevented this?

Conclusion

difference between these types of friction ridge skin impressions and fingerprints is that files of palm prints or footprints are not maintained, because these impressions are less frequently encountered than fingerprints. Generally, investigators must develop one or more suspects, then arrange to collect inked palm or foot impressions as knowns for comparison. The meth- ods used for comparison and the criteria for conclusions are the same as for fingerprints.

Conclusion Patterns are an important class of evidence. Identification patterns refer to the mental images used to classify objects in the environment. Individualization patterns can be physical pat- terns or impressions. The most commonly seen impressions are footwear and tire tracks. Reconstruction patterns help investigators form theories about events that took place in the past, based on the physical evidence record.

Pattern evidence is collected by photography, lifting, and casting, as appropriate. It is ana- lyzed by comparing a questioned impression with a known impression or object. A proper comparison requires that only like impressions be compared (positives, negatives, left, right, etc.). Some pattern evidence can sometimes be individualized.

Fingerprints are an important category of evidence and have a lengthy history of use as a means of personal identification. Automated fingerprint identification systems have enabled the storage and search of single fingerprints and have rendered 10-print cards and classifica- tion systems obsolete. At scenes, visible, plastic, and latent prints can be found. Latent prints require some visualization techniques to make the ridge detail suitable for comparison. There are physical, chemical, and instrumental methods for developing latent prints. Questioned fingerprints are compared with known prints, and examiners can often individualize the print to a person or exclude a person as the source. Sometimes prints are not suitable for comparison, or there is insufficient detail to reach a conclusion. There has been discussion about the scientific basis for fingerprint individuality and whether individualization is justi- fied in fingerprint comparison, particularly with questioned partial prints. Palm prints and footprints are sometimes encountered at scenes, and they may be compared to knowns in the same way as fingerprints.

Key Ideas

• There are patterns for identification, for individualization, and for reconstruction. • Important patterns for individualization include physical matches, as well as imprint

and indentation markings, of which footwear and tire impressions may be the most common.

• Fingerprints are an important class of physical evidence and an example of a bio- metric identifier.

• AFIS systems enable rapid search and retrieval of single fingerprints. • Latent fingerprints require visualization or processing steps in order to be suitable

for comparison. • There is a method for fingerprint (and other friction ridge print) comparisons called

ACE-V, which describes the steps an examiner follows to compare questioned and known prints.

Conclusion

• Fingerprints are individual. With very rare exceptions, identifications or exclusions can be made following a comparison by a qualified examiner.

• Footprints and palm prints are compared in the same manner as fingerprints.

Critical-Thinking Questions

1. In a criminal aggravated assault case, the accused ripped off the victim’s dress, and in the process, a piece became completely separated and got stuck on the back of the perpetrator’s shirt. The police later recovered the shirt, which still had the fragment of dress on it. Imagine that you are the lab examiner, comparing the evidential frag- ment to the dress. This is a summer-weight, light material with a distinctive, decora- tive pattern on it. The fragment lines up almost perfectly with a missing area on the victim’s dress. Color and pattern are the same. Thread count is the same. It definitely could be the missing piece. How would you testify to this finding?

2. In a criminal case, a suspect is thought to have kicked in a metal door while wearing a sneaker. The police successfully use an electrostatic dust lifter to lift a good dust print of the sneaker from the door. They also have a suspect and the sneaker they think probably made the mark. How would you, as the examiner, make the “known” sneaker impression to compare with the dust print?

3. A government agency is willing to fund a study to establish that fingerprints are really individual. How would you design this study? Describe the study design, the results that might be expected, and the conclusions that could be drawn from them.

4. In a homicide case, the police find a good bloody footprint on a bathroom floor tile. They think the footprint belongs to the perpetrator. They have a suspect in custody, but they cannot prove he was at the scene at the time of the crime. You are the exam- iner and are given the tile with the questioned footprint on it. How would you tell the police to collect the known footprints from the decedent and from the suspect? Do you think the police need a search warrant to collect the known footprint from the suspect?

5. You are the fingerprint expert witness in a criminal trial. An object from the crime scene had a good latent print on it, and you were able to match the latent to the known print from one of the defendant’s fingers. You have testified that the latent fingerprint came from the defendant. The defense lawyer now says to you the fol- lowing: “The police had a 10-print card on file containing the defendant’s finger- prints. At the time the police arrested the defendant, they had very little evidence that he was actually at the scene, but they were convinced he was their guy. Suppose they took some lifting tape and carefully lifted off one of the prints from the 10-print card, then used that tape to place the ‘latent print’ on the object from the scene that was submitted to you for examination. Do you concede that this scenario is possible? If so, would you agree that the latent match to the defendant does not then prove that he was actually at the scene?”

Key Terms accidental An individual characteristic in an item of footwear, a tire, or other object that occurs as the result of wear and expo- sure and that can be detected in an imprint or indentation of the item.

Analysis, Comparison, Evaluation, and Verification (ACE-V) The process followed by fingerprint examiners in their compari- sons of known and questioned fingerprints, as well as footprints or palm prints.

Conclusion

biometric Literally, any biological feature that might be used to distinguish people. Fingerprints are an example of a biometric identifier.

bite mark A mark made in a soft receiv- ing surface by human teeth. Human teeth, and thus the mark patterns they make, are believed to have individual characteristics.

direct A physical match of pieces of a ran- domly fractured solid material, such as glass or plastic, in the manner of a jigsaw fit.

exclusion A conclusion by an examiner that a questioned specimen cannot have origi- nated from a known specimen with which it has been compared.

identification In pattern evidence com- parisons, this term means individualization, a conclusion that the questioned specimen originated from the known with which it was compared.

impression Any mark made by an object impressing its shape and form into or onto another object or surface. Impressions can be imprints or indentations.

imprint An effectively two-dimensional impression.

inconclusive In pattern evidence compari- sons, this conclusion means that there is not sufficient information to draw a definite conclusion; that is, we cannot say for sure whether the questioned is excluded or there is an identification.

indentation A three-dimensional impression.

indirect A physical match of pieces of a nonsolid item or object that has been cut or torn, or of a solid object that fractures in such a way that the pieces cannot be directly realigned.

latent Literally, “hidden.” A latent finger- print is one that requires processing or development in order to be visible and suit- able for comparison.

minutiae (singular: minutia) The individu- alizing characteristics of a fingerprint pat- tern. Primarily, examiners use dots, bifurca- tions, and ending ridges.

ninhydrin A chemical that reacts with amino acids to form a visible, violet-col- ored product. It is used to visualize latent fingerprints.

patent Literally, “visible” or “obvious.” A patent fingerprint is visible.

plastic An indentation fingerprint that has been impressed into a soft receiving surface so as to have depth.

striation A sliding tool mark, resulting from one surface sliding on another and thus creating a mark.

superglue A commercial adhesive, chemi- cally a cyanoacrylate ester, which can be used to develop latent fingerprints by fum- ing the glue onto the print residue.

10-print card Formerly, fingerprints from individuals were collected on cards format- ted to hold information about the person plus inked fingerprints from all 10 fingers. The 10-print card was the basis of classifi- cation systems, and the cards were kept in physical files.

visible Able to be seen. A visible print can be seen with no development or processing.

Conclusion

Web Resources Example website for AFIS: http://www.bio-metrica.com/SYS_B_CRIMINAL_AFIS.php

OSAC FRS: http://www.nist.gov/topics/forensic-science/friction-ridge-subcommittee

Federal special report on the case of Brandon Mayfield: http://www.justice.gov/oig/special/s0601/PDF_list.htm

The proceedings of a major meeting on impression, pattern, and trace evidence and its util- ity and interpretation: Jones, N. S. (Ed.). (2018). 2018 impression, pattern and trace evidence symposium. Research Triangle Park, NC: RTI Press. https://doi.org/10.3768/rtipress.2018.cp.0006.1805

More discussion of bite mark comparison reliability: https://www.washingtonpost.com/news/the-watch/wp/2016/02/01/the-latest-from-the- world-of-bite-mark-evidence/?noredirect=on&utm_term=.035694c1ccd2

http://www.bio-metrica.com/SYS_B_CRIMINAL_AFIS.php

http://www.nist.gov/topics/forensic-science/friction-ridge-subcommittee

http://www.justice.gov/oig/special/s0601/PDF_list.htm

https://doi.org/10.3768/rtipress.2018.cp.0006.1805

https://www.washingtonpost.com/news/the-watch/wp/2016/02/01/the-latest-from-the-world-of-bite-mark-evidence/?noredirect=on&utm_term=.035694c1ccd2

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