The Science of Evidence

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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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11DNA Analysis

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

▪ Describe DNA, its functions, and where it is found in the body.

▪ Explain the process of typing and profiling DNA, as well as the strengths and limitations.

▪ Discuss DNA profile databases and their significance.

▪ List how DNA can apply to different types of cases.

▪ Summarize newer DNA technologies.

▪ Describe how human remains are identified.

Section 11.1The Nature of DNA

Introduction Now that we have seen how biological evidence is collected, preserved, and initially analyzed, we can take a closer look at DNA analysis and profiling. DNA typing has been available in some form since about 1985, but it did not come into wide use in forensic labs until the 1990s. For most of the 20th century, forensic scientists used blood types and other blood markers (such as isoenzymes and serum proteins) to narrow down the possible sources of blood and body fluids. There are four blood types: A, B, AB, and O. When blood is transfused, the donor and recipient types ideally match. Under emergency conditions, O blood can be transfused to anyone, and AB persons can receive blood from anyone. Methods were developed to deter- mine blood types and other protein markers from dried blood and body fluid stains. However, these systems do not have enough genetic variability to narrow down the possible suspects. At times the result was no better than 50%, though sometimes a set of blood and other pro- tein marker types could be narrowed down to one in several thousands of people. Still, even under the best circumstances, many people in the population fell into the same group or com- bination of groups. With DNA typing, the results are much more individualizing, and one can have more confidence in a DNA match than was ever possible before.

11.1 The Nature of DNA Blood groups and deoxyribonucleic acid (DNA) can be used to individualize biological evi- dence because they reveal information about the genetic makeup of the person. Genetics is the science of inheritance in all living things. Blood groups and DNA are inherited, and we can understand their inheritance among individuals, in families, and in larger populations. The proportions of people expected to have a set of blood groups or a certain DNA profile are con- stant and predictable in most populations most of the time. If the proportion of a population expected to have a certain pro- file is very low, that means there will be only a small number of people who have the profile.

Sometimes, the probability of a chance duplicate—someone with an identical profile—is so low that it is likely that only one person has the profile. However, it cannot be scientifically proved that the profile belongs to only one person. A DNA expert goes to court to discuss the chances that the profile is duplicated in the popu- lation. For example, say John, the suspect in Mary’s assault case, has a bloodstain on his clothes. John and Mary do not know

Creatas Images/Creatas/Thinkstock DNA varies enough between individual people enough to be differentiated, except in the case of identical twins. Do you think this reinforces stereotypes about twins being exactly the same?

Section 11.1The Nature of DNA

one another. If John assaulted Mary, the bloodstain on his clothing could be Mary’s blood. In the lab both John’s and Mary’s DNA will be profiled. Their profiles will be different. Next the clothing bloodstain is profiled and compared with each profile. Suppose it matches John, proving the stain is from his own blood. Let’s also suppose that John told the police he had a nosebleed and bled on his clothes. The DNA typing corroborates his story and provides no evidence that he assaulted Mary, but it also doesn’t prove his innocence. Suppose the blood- stain profile matches Mary. This result provides physical evidence that John assaulted Mary. At a minimum, he has Mary’s probable blood on his clothes. Imagine, instead of the nosebleed story, John tells the police that he happened upon the assault scene and helped Mary up from the street to be a Good Samaritan. If Mary did not see her assailant and does not say that John is the person who assaulted her, this result would provide an innocent explanation for the bloodstain. Now consider a third result: The DNA profile of the bloodstain matches neither person. John might or might not make a statement to police about how the blood got on his clothes, but whether he does or not, the DNA results do not implicate him. However, they also do not prove he did not assault Mary.

This example is typical of many forensic cases. DNA results identify whose blood or body flu- ids are present in stains. However, they do not explain how the blood or body fluids got there, and they do not establish guilt or innocence. The combination of DNA results, the fact pattern of the case, and the credibility of statements made to authorities help judges and juries draw inferences about the events that occurred in order to deliver a verdict.

How DNA Works Every person begins life as a single cell. That cell is the result of the union of a father’s sperm cell and a mother’s egg cell. The sperm and the egg each have a random half of the DNA of the father and mother, respectively. When they combine—that is, when the egg is fertilized—the new cell has a complete set of DNA, half from each parent. Because the sperm and the egg have a random half of the parental DNA, every sperm and every egg is different. Therefore, brothers and sisters will look more alike than strangers, but they are not exactly the same. Sometimes twins or triplets can be conceived. If they are from different sperm and egg cells, they will be as different as any other brother or sister and are called fraternal twins or trip- lets. Other times, the fertilized egg divides into two before beginning the process of develop- ment, creating identical twins. These twins have exactly the same DNA at conception and it was traditionally thought that they could not be differentiated by DNA typing. However, it was recently discovered that, as identical twins grow, each sibling develops a unique set of genetic mutations (Eveleth, 2012). This means that it may in fact be possible to differentiate the DNA of two identical twins.

DNA is packaged in special structures called chromosomes, which are the inherited physical structures that carry DNA. Humans have 46 chromosomes, 44 of which consist of 22 pairs. The other two are called X and Y, or sex chromosomes, which determine a person’s sex. Males are XY, and females are XX, as shown in Figure 11.1.

Section 11.1The Nature of DNA

Figure 11.1: Human karyotypes

Humans have 46 chromosomes, which consist of 22 pairs and sex chromosomes. Males have XY, while females have XX.

Science Photo Library/Superstock

Chromosomes are very small. You need a microscope to look at them. And they are not all neatly arranged like in Figure 11.1. There are techniques for staining the chromosomes, tak- ing a good picture of them, enlarging the picture, then arranging them like they are in Figure 11.1. The chromosome makeup of an individual is called a karyotype. Sometimes doctors

1 2 3 4 5 6 7 8 9

10 11 12 13

19 20 21 22

14 15 16

XYXY XXXX

Think About It

A strange and unusual case of disputed paternity came up in a courtroom. A woman gave birth to a child and petitioned a court to order the father to pay support. In the case, she admit- ted that she had sexual relations with identical twin brothers around the time the child was conceived. The sexual relations were close enough in time so that either brother could be the father. Do you think DNA typing will help us figure out which brother is the father? Why or why not? If you were the judge in this case, what would you do about the child support?

Section 11.1The Nature of DNA

want to look at someone’s karyotype to see if the person has a chromosomal abnormality. One such abnormality that most people know about is Down syndrome. Down syndrome patients have three, instead of two, number 21 chromosomes.

As shown in Figure 11.2, DNA is wound up in the form of a double helix that is made up of a series of unit molecules that are called adenine, thymine, cytosine, and guanine, and are referred to as A, T, C, and G, respectively. These are the letters of a genetic alphabet. There are approximately 3.5 billion of these unit molecules in a person’s DNA. This alphabet has the ability to give a cell instructions. DNA primarily tells cells what proteins to make and when to make them. DNA, therefore, controls cell function. When someone refers to DNA sequencing, it means that the order of the string of letters has been determined. By 2001 scientists had successfully sequenced one person’s entire DNA (called the human genome) for the first time.

For forensic purposes, it is not necessary to sequence a person’s entire DNA in order to “indi- vidualize” the person. There are some regions of DNA that contain repeat letter sets, such as “AACC-AACC-AACC” or “ACTG-ACTG-ACTG-ACTG-ACTG,” and so forth. Most people have differ- ent numbers of these repeated sets in their DNA. If scientists can isolate a region of DNA that includes the repeat letter sets, then the number of repeats is related to the size of the frag- ment. Forensic scientists have concentrated their efforts on these short repeated sequences. Determining the size of the repeat sequence fragment at a particular location in DNA, or locus (its plural name is loci, which is Latin for “places”), is often called typing. If the DNA analysis involves figuring out the repeat sequence numbers at several different loci, the result is a DNA profile. DNA profiling can also determine if the DNA came from a male or a female.

Figure 11.2: DNA double helix

On the right is DNA in the familiar form of a double helix, while the left shows it unwound. DNA is made up of molecules that pair up: adenine with thymine, cytosine with guanine.

G C C

C G

T A

A T

C G

G C

T A

C G

A T

Section 11.2Typing and Profiling DNA

From “What Is DNA?,” by Council for Responsible Genetics, n.d. (http://www.councilforresponsiblegenetics.org/geneticprivacy/ DNA_sci_1.html).

DNA’s Location in the Body The cell nucleus, a membrane-bound structure within a cell, contains the chromosomes, which in turn contain the DNA. When a cell divides to make two daughter cells, the nuclear DNA is replicated, and each daughter cell receives an exact copy.

Thus, even though people are made up of billions and billions of cells, every single cell has the same copy of DNA. There are two exceptions to this general rule. The first exception is repro- ductive cells, or sperm cells (for males) and egg cells (for females). These cells form through a special kind of cell division that selects a random half of the DNA. The second exception is red blood cells. During their formation, they lose their nuclei, and therefore they do not contain DNA. Red blood cells are the most plentiful cell in blood; there are approximately 5 million of them per µL of blood (µL is a symbol for “microliter,” a unit of volume used by scientists; micro means “millionth,” so there are a million microliters in one liter).

In blood, DNA comes from our white blood cells, as noted in Chapter 10. There are around 7,000 or 8,000 of these per µL of blood. However, it is not necessary to col- lect blood for DNA typing from known persons. Every other tissue in the body has nucleated cells, and DNA can be obtained from the cells. It is very common to do a cheek or buccal swab to collect cells for DNA typing, as was discussed in Chapter 10.2. Sometimes, investigators collect tissues other than blood, semen, or vaginal swabbings. DNA can often be typed from any human remains if they are not too decomposed—sometimes even from bone. This is helpful in mass disaster cases or when bodies have been dismem- bered and/or burned.

The next section will cover typing and profiling DNA. Usually, when people are talking about DNA typing or profiling, they are talking about nuclear DNA.

11.2 Typing and Profiling DNA DNA typing consists of steps that take several days to complete to obtain a DNA profile. Even a simple case may have many specimens submitted for DNA typing. Laboratories are overwhelmed by DNA cases, and it can sometimes take months for analysts to begin pro- cessing a case.

Frentusha/iStock/Thinkstock Even when cells divide, like in mitosis, DNA is not lost but is replicated into the new daughter cell. How does this knowledge increase the validity of DNA analysis?

Section 11.2Typing and Profiling DNA

Steps in DNA Typing and Profiling The first step in the process is called isolation (or extraction). DNA must be separated from the cell and tissue material in which it is found in order to be analyzed. There are several dif- ferent techniques for accomplishing this task. The method commonly used by forensic labs involves mixing the DNA with organic solvents (phenol and chloroform), then capturing it on a membrane from the phenol phase. From there, it can be dissolved in a buffer solution. These days, it takes only a small amount of DNA to complete the analysis—in most cases DNA from 100 cells will be enough. Results may sometimes be obtained with even fewer cells. If you consider that blood generally contains about 7,000 white cells per microliter, a fraction of a microliter is enough for typing. As a visual, about 10 microliters of blood would make a bloodstain on absorbent cotton cloth around the size of your pinkie fingernail.

Once DNA has been extracted from the specimen, some additional steps are necessary for further analysis.

The next step is quantitation (or quantification), which means determining how much of something is present. Forensic scientists must determine how much DNA is available for the next steps. Today, in the process of quantitating DNA, results can show that it is human and how much human DNA is there. The following sections will talk about PCR, or polymerase chain reaction. A variant of this procedure known as real-time PCR is used for quantitating human DNA. Only human DNA can be typed and profiled, because human typing tools do not work on other animal or plant DNA. Their genetic makeup is completely different, as you would expect, and the PCR step doesn’t work for other species. Many specimens have bacteria in them, and the isolated DNA will be a mixture of human and bacterial DNA. The bacterial DNA does not interfere with testing. This quantitation step tells the analyst how much human DNA is available for the rest of the analysis.

You may recall from Chapter 10 that the steps in DNA typing contain this step, in which you find out how much human DNA is present, and that this is a species test. If you get human DNA out of a specimen, then there must have been human cells in that specimen. However, if you don’t find any human DNA, this pro- cedure gives no information about what other species the specimen may have come from.

The last step involves DNA typing. DNA typing for forensic purposes began in the mid-1980s and has gone through several technological stages. The most important was the development of a technique called polymerase chain reaction (PCR). Today PCR is used to amplify a DNA specimen for typing.

Polymerase Chain Reaction PCR is a process of making a large num- ber of copies of a small region of DNA. The

age fotostock/SuperStock Improvements to science and technology have had a huge impact in forensic science. How has the development of the PCR technique been beneficial?

Section 11.2Typing and Profiling DNA

copying process is the same one that cells use to replicate themselves. As noted earlier, when a cell divides, it has to replicate all its DNA. Here, we only want to replicate a small segment of the DNA. In the 1980s scientists discovered a DNA-copying enzyme in bacteria whose activity can be controlled by temperature. This fairly simple discovery revolutionized DNA research and forensic DNA typing. Forensic scientists could now make large numbers of copies of a small DNA region and thus be able to analyze extremely small amounts of specimen. PCR is also sometimes called amplification, and this amplified DNA is used for the rest of the analy- sis. Copying these small DNA regions involves short DNA sequences called primers, which are synthesized. The sequence of the ATCG letters in the primers dictates which region of DNA will be copied. The PCR process goes through a cycle of heating, cooling, and reheating to make one copy. Every time this cycle is done, the number of copies doubles. In forensic work, a typical analysis uses 25 cycles. Doubling the number of copies every cycle for 25 cycles results in around 33 million copies of the DNA segment.

The value of a process like this is quite clear for forensic applications. With only a very small quantity of biological evidence, the copying process enables scientists to make enough of the desired DNA segment for typing. PCR is the reason forensic scientists can type DNA in such small specimens.

Short Tandem Repeats Recall that we discussed the small regions of DNA that contain repeat segments of A, T, C, and G. One example was . . . AACC-AACC-AACC. . . . This four-letter segment is repeated three times. These repeats are always head-to-tail. Think of the “CC” end as the “head” and the “AA” end as the “tail.” The “AA” end of one repeat is never next to the “AA” end of another one. The DNA regions (loci) chosen for forensic work have four- or five-letter repeat units and are thus called short tandem repeats (STRs).

Typing In the PCR step, multiple copies were made of the small regions of DNA in which we are inter- ested. In practice, this is all done in the same reaction tube. Using clever molecular strategies for positioning the primer molecules and adding dye molecules to them, all these molecules can be passed through a thin capillary tube, through which they are driven by an electric field. In the capillary, they are separated by size. The capillary is part of a special DNA analyzer instrument. This instrument also contains special analyzing devices that can “see” each DNA fragment as it passes and can tell which dye is on it. The instrument can be calibrated with DNA fragments of known size so that it also knows how big each fragment is. In this way the instrument software figures out how many repeats there are at each DNA locus on each chro- mosome. Remember that everyone has a pair of every chromosome. The number of repeats at a region on it might be the same or different (depending on whether the person’s maternal and paternal chromosomes had the same number of repeats).

Thirteen loci were initially chosen for forensic DNA typing. The FBI, in collaboration with forensic DNA testing labs, expanded the number to 20 loci on January 1, 2017. The analysis gives typing at every locus (every one of the 20 regions). The analysis also includes a gender

Section 11.2Typing and Profiling DNA

marker—it indicates whether the specimen is from a male or female. Thus, a DNA profile is the determination of the number of repeated units a person has on each of his or her two chromosomes at each of the 20 regions of DNA, as well as an indication of gender. A set of DNA types constituting a DNA profile will be illustrated later in this chapter.

Individualizing Specimens A DNA profile using 20 separate STR regions of DNA is highly unlikely to be duplicated by another person in the population. That is, there is probably only one person with the profile, with the exception of identical twins. Also, family members have much more similarity among their DNA than they have with unrelated people. Casework reporting typically refers to the chances of duplication among unrelated people.

Forensic scientists carry out population studies—profiling a number of people from a popu- lation—to obtain the data to determine how common or rare a profile is. Many population studies have now been conducted. Another consideration is racial/ethnic variation. The frequencies of DNA types can vary among major racial or ethnic groups. One of many such studies is that of Budowle, Shea, Niezgoda, and Chakraborty (2001). Generally, therefore, population studies are conducted separately and compiled for different groups. The major groups are Caucasian, African American, and Hispanic, but there are also studies for various Native American groups, Chinese Americans, and so on. Since the ethnicity or race of the actual depositor of a questioned stain is unknown, experts typically provide calculations for all available groups.

The probability of chance duplication in a DNA profile works a bit like flipping a coin. If a coin is not rigged, there is a 50% chance of getting heads or tails on one flip. If the coin is flipped twice, what are the chances of getting heads twice? The answer is 25%. That answer is cal- culated by multiplying 50% by 50%, or ½ x ½. The individual chances of getting heads on a single flip are multiplied together because the flips are independent; the second flip is not influenced by the first flip. If the coin is flipped three times, what are the chances of getting heads three times? They are ⅛ (which is ½ x ½ x ½). As the number of flips increases, the chances of getting only heads (or tails) on every flip decreases.

The regions of DNA that are used in DNA profiling are inherited independently of one another. Therefore, the inheritance of genes at one location doesn’t influence the inheritance at the second or third, and so forth. In order to estimate how common or rare a profile is, the indi- vidual type frequencies must be multiplied together as with the coin flip trials. This is called the product rule in forensic DNA typing.

A DNA Profile and Its Rarity in the Population An example of a DNA profile is shown in Table 11.1. For simplicity, this table has only 9 regions (loci) instead of all 20 that are available. The “DNA type” for the locus D3S1358 is 16,16. The “DNA profile” is all the loci with their associated types. As you continue to read, this table will be a helpful reference as each column is described.

Section 11.2Typing and Profiling DNA

Table 11.1: A DNA profile and its rarity in the population

DNA locus Type Frequency Combined frequency Combined frequency: 1 person in

D3S1358 16,16 0.2867 0.0822 12

D5S818 11,12 0.2387,0.3484 0.0137 73

D7S820 8,14 0.1993,0.0033 0.0000180 55,607

D13S317 11,12 0.3258,0.3613 0.000000423 236,202

FGA 20,24 0.0686,0.1536 0.0000000892 11,208,266

VWA 16,19 0.2677,0.0516 0.00000000246 405,705,024

D8S1179 13,16 0.2194,0.0742 0.0000000000802 12,460,626,024

D18S51 13,16 0.0613,0.1774 0.00000000000175 572,922,365,322

D21S11 30,30 0.1710 0.0000000000000510 19,593,118,064,452

Each DNA locus used for profiling has a name. Most names begin with the letter “D,” which is shown in the DNA locus column. There are nine regions (loci) of DNA shown in this table.

The Type column contains the number of repeats of the core repeat sequence that the per- son has on each chromosome at this DNA locus (this is a DNA profile of one of this book’s authors). As noted above, these core repeat sequences are four or five letters. In the case of D3S1358, the core repeat sequence is TCTA. This information is obtained from sequencing studies. Table 11.1 shows that at the locus D3S1358, the person has 16 repeats of TCTA on each chromosome. Other people will have different numbers of TCTA repeats on their chro- mosomes at the D3S1358 locus. At the next locus, called D5S818, there are 11 repeats on one chromosome and 12 repeats on the other. As you can see, a person may have the same or dif- ferent numbers of repeats on the two chromosomes, because one chromosome is inherited from the mother and the other from the father.

Each region (locus) has a different number of possible repeats. At D3S1358, a person can have 12 different possible numbers of repeats, such as 12, 13, 14, 15, 16, and so forth. This number can be different on each chromosome. Thus, someone can be 12,12 or 12,13 or 12,14, and so on. The total number of combinations is 144. Therefore, there are 144 possible “types” in the population at this one region. Similarly, D5S818 has 12 different possible numbers of repeats also, which means there are 144 possible types at this region, just like the D3S1358 region. As more and more regions are profiled, the number of possible types that could be in the profile grows quickly.

The Frequency column is where the information from population studies can be used to indi- vidualize specimens. The numbers in this table come from Caucasian population studies com- pleted in the population of Illinois in the United States (Budowle et al., 2001). The top row in the column tells us that of all the possible numbers of repeats at D3S1358, 16 repeats is seen in 0.2867, or 28.67%, of the total number of D3S1358 genes in the population. Moving down one row, at the D5S818 locus, 11 repeats are seen in 0.2387 of the total and 12 repeats are seen in 0.3484 of the total. The combined frequency of the type in the population can be cal- culated from these numbers. That is, by knowing the frequency of the 16 repeats at D3S1358, we can compute how often we will see a 16,16 person. Similarly, by knowing the frequency of the 11 and 12 repeats at D5S818, we can compute how often we will see an 11,12 person,

Section 11.2Typing and Profiling DNA

and so forth. These calculations come from genetic theory, and the details are not essential to understanding this table.

The Combined frequency column does for the DNA profile what we did for the coin flips ear- lier in the chapter. The difference is that each one of these DNA regions is not a two-sided coin but a many-sided coin, if you will. Looking at the top row, this person with the type 16,16 at D3S1358 is seen in about 0.0822 of the population. Now look at the final column. The final column simply converts the fraction of the population to a “1 in so many people” number. This first row says that 0.0822 of the population is about 1 person out of 12. When the population was sampled and typed for the population study, a 16,16 person was found in about 1 of 12 people, which is relatively common. Most people would not vote to convict someone of a crime because of a shared type that is common in 1 of 12 people. Now, move down to D5S818. How common is a person who is 16,16 at D3S1358 and 11,12 at D5S818? About 1 in 73 people, which is still not very individual. But as more regions are typed—that is, as we move down the rows of the table—the numbers, or the probability of finding another individual with the same DNA typing, become smaller and smaller. When the first six regions are included, the profile is expected in about 1 in 405 million people. As of 2018 there were about 325 million people in the United States. By the time the types at all nine regions in the table are factored in, the profile is expected in only 1 in approximately 19 trillion people. This number is much higher than the population of the earth. Therefore, this tells us that it is not very likely there is another person sharing this profile. Remember too that these data apply only to Caucasians, and there are far fewer Caucasians than total people.

Note that this calculation assumes unrelated people. If people are related, there is a much greater chance of shared genes and DNA types; that is, there is an increased chance of a dupli- cate. Also note that only 9 of the potential 20 regions that are normally included in a DNA profile were entered in the table. If the other 11 were calculated, the probability of chance duplication would become even smaller. Under some circumstances, scientists from the FBI Lab now testify that “the stain originated from a particular person to a reasonable degree of certainty.” They don’t say that it definitely came from the person, because there is a chance that there is someone else who has the same profile. Also note that in the profile used in this illustration, there is no gender marker. With full DNA profiles, there are results from all 20 loci plus a male or female result.

Think About It

Let’s say the results in the illustrative Table 11.1 were obtained in an actual case. A bloodstain thought to have come from the suspect had this profile, and so did the suspect. The expert could testify in two different ways:

1. The DNA profile of the bloodstain is identical to the DNA profile of the suspect, and the expected chance of duplication in the population is around 1 in 19.6 trillion.

2. To a reasonable degree of scientific certainty, the evidence bloodstain originated from the suspect, assuming the suspect does not have an identical twin.

Which one of these statements do you think would be most helpful to the jury in understand- ing the significance of the DNA type match, and why? Do you think the statements are equally scientifically justifiable? Why or why not?

Section 11.3Databases and CODIS

Strengths and Limitations of DNA Profiling You can see how powerful DNA technology can be in identifying individuals and in excluding those who don’t match the profile. From the beginning, and even now, forensic DNA technol- ogy has been accompanied by much publicity in the popular press and coverage on popu- lar programs like CSI. It is important that you understand the limitations of DNA technology along with its strengths.

Contrary to popular belief—and often, media impressions—DNA profiling matches and non- matches do not equate to guilt or innocence. People may say “DNA proved the guy innocent,” but this is untrue. It may have proved that his DNA was not where they think it should have been if he committed the crime and that someone else’s DNA was there instead, but that is all. The actual verdict of guilt or innocence is determined by a judge or jury.

A number of individuals who were convicted before DNA technology was available have been released based on postconviction testing. Some of these men were on death row. The Inno- cence Project in New York and related efforts in many states have helped press the idea of postconviction testing in cases in which biological evidence remains and DNA technology was not available at the time of the original conviction.

DNA profiling is not always as straightforward as it may seem. It is a complicated technology, and there are many things that can go wrong along the way. Labs take precautions to make sure everything is working correctly, but sometimes results can be ambiguous. Mixtures can be particularly difficult to interpret, for example. And sometimes comparably qualified experts disagree over the interpretation of the same set of results.

11.3 Databases and CODIS DNA types and profiles are, in the end, just a bunch of numbers. Numbers are easily stored in computer databases, which help make DNA a powerful technology for forensic work. Not only are the profiles expected to be highly individual, but they can be stored and saved. Once that has been done, the database can be searched for any profile, and if it is found, there is a high degree of certainty as to the person’s identity.

CODIS is the DNA database in the United States. When DNA typing became available to foren- sic labs, and the importance of DNA databases was recognized, the immediate question became: Whose DNA profiles should be stored in the database? The building, maintenance, and authority to search DNA databases are matters of law, so there had to be federal and state laws that specified whose DNA profiles could be databased. It has been found that many per- sons convicted of crimes will reoffend after their release from incarceration (Bonczar & Glaze, 2008). Because of this information, initially the idea was to store the DNA profiles of convicted

Think About It

Can you think of other strengths and limitations of DNA profiling?

Section 11.3Databases and CODIS

persons in the database. The emphasis was placed on sex offenders, because DNA profiles of the male can often be devel- oped from sexual assault evidence. The idea was that if the person’s DNA was in the database and he committed another sex crime, he would be quickly identified.

DNA databases have been very helpful to law enforcement in developing suspects in crimes by providing identifying DNA profiles. This success has led legislatures to expand the range of persons whose DNA goes into the database. Many states now have “all felony” conviction DNA databasing. A few states permit juveniles’ DNA profiles in the database. More states are passing laws to enable the databasing of DNA from arrested persons (see http://www.dnaresource.com). However, there are even more cases in which DNA could be databased. For instance, many law enforcement officials feel that suspects in investigations should be included as well.

When a DNA profile is developed from an evidence specimen and entered into CODIS and the profile is found, it is called a CODIS hit. When such a result is obtained, the lab acquires a new specimen from the individual identified by the database hit and does the profile again. This practice is a quality assurance measure.

The Database Debate Databasing raises some issues for debate. One point that is often discussed is the extent to which DNA databasing becomes an invasion of privacy. A 2013 Supreme Court decision (Maryland v. King, 2013) upheld the practice, arguing that profiling DNA and adding it to a database is no more intrusive than taking fingerprints and keeping them on file. Some people are concerned that law enforcement may want to dig deeper into the DNA, at least in some cases, as advances in knowledge and technology enable them to do so. Recall the discussion of how DNA controls cell function. In theory, DNA sequences can tell analysts a great deal about a person. DNA analysis has the potential to provide health and health-related information, information about a person’s appearance (such as eye color), and perhaps information about a person’s ethnicity to investigators. However, there is still much to be learned about how DNA sequences can determine a person’s health and well-being. Regarding this issue, law enforce- ment states the point is moot. The STRs used for DNA typing and profiling included in the database have no known function. In fact, a large portion of DNA has no known function. As a result, the forensic DNA profiles are useful only for identification—similar to fingerprints.

Storing Profiles From reading how DNA can be individualized, you can see that the more loci typed, the greater the individuality of the profile. At the beginning of DNA typing technology in law enforcement,

Khue Bui/Associated Press Databases are a centralized way to store data that can be available to many people in different areas. Do you think the formation of CODIS was beneficial?

Section 11.3Databases and CODIS

policy makers had to make some decisions. How many loci should be used? The more loci used, the more expensive it is to type, enter the data, and maintain the database. On the other hand, the fewer used, the more chance duplicates there will be, which is undesirable. This would be an inefficient use of the database, as police might have to locate 50 or 100 people or more for every profile that hit.

Law enforcement’s answer was to use more loci in order to have more individuality and almost no duplication. Twenty loci are enough to accomplish that goal, and this is the num- ber that is used today. An important aspect to databasing information is that all laboratories must follow the same protocol. Everyone must profile the same loci and trust that all other analysts obtain the same result from the same specimen. Otherwise the database will not be useful. The FBI Laboratory coordinated the effort, and the database resides there. The big, national database is called National DNA Indexing System, or NDIS. Each state has its own CODIS database called State DNA Indexing System, or SDIS. States have the option of having records in their databases that are not sent to NDIS, but this is not a common practice. Local city or county law enforcement can have a database too (LDIS). Local profiles are generally uploaded to state databases, which are then uploaded to NDIS. NDIS requires a minimum number of loci (8 for forensic specimens, all 20 for profiles from persons) in a profile and has a number of other requirements for laboratories wishing to upload to it or conduct searches. As of May 2018, NDIS contained over 13.3 million offender profiles, over 3.1 million arrestee profiles, and over 858,000 forensic profiles (FBI, 2018).

When a laboratory receives biological evidence, processes it for DNA, and obtains a profile, it needs a known profile with which to compare the evidentiary one. In some cases it might be clear from the fact pattern that the evidentiary DNA came from one or more known suspects or from a victim. The lab would then develop DNA profiles for those people and make the comparisons. Sometimes, though, there is no suspect. Consider a sexual assault case in which a woman is assaulted by someone wearing a ski mask. She cannot see her assailant’s face and therefore cannot identify him. However, the lab is able to obtain a male DNA profile from the semen. Now investigators have a DNA profile of a person, but they don’t know who it is. Let’s say the lab searches the national database and does not find the profile. The analyst can then perform a search in a special database that houses the profiles of unknown suspects, called the forensic file. There is a database in NDIS dedicated to missing persons as well.

If a lab develops a DNA profile but doesn’t know whose it is, the analyst will search the NDIS convicted offender database. If the profile is found, it is called a hit. The analyst can then look up whose DNA was hit and obtain the person’s identity. As of May 2018 there have been over 422,000 hits in the database (FBI, 2018).

The lab can also search the forensic file. What if there is a hit here? It means that the suspect in the current case came up in another case but is still unidentified. This is useful because investigators from the different cases can compare notes. This often occurs across states, when the investigators have no other way of knowing their cases are connected. Even locally, police can have a series of cases that they have not connected to a single offender.

You can probably see why many in law enforcement favor storing more profiles in the data- base. The more profiles there are, the more likely it is that there will be a hit on a search. In this context, there are arguments about whether profiles should be removed from the

Section 11.3Databases and CODIS

database under certain circumstances. For example, say a state decided to put DNA profiles of suspects in the database. Should these profiles be removed once the person is no longer a suspect? It is a complicated task that requires effort and money.

Familial Searching An additional important aspect regarding database searches is familial searching. For example, say a lab searches the databases and doesn’t find a match, so the analyst goes a step further. A search is run for partial matches—that is, people with similar profiles, namely relatives. Suppose for a moment that analysts have your profile, but your profile is not in the database. However, your brother’s profile is. He was convicted of a crime, and his informa- tion is stored in the system. In a familial search, the lab could find your brother. Analysts and investigators could then determine that he has a sibling (you) and possibly figure out that you are the person they are looking for.

In 2010 Los Angeles police solved an old and difficult serial murder case this way.

For 22 years, there was a serial killer operating in Los Angeles dubbed the Grim Sleeper. The victims were mainly young, Black prostitutes along a stretch of Western Avenue in Los Ange- les. From 1988 to 2002, there were no crimes that fit the killer’s profile. In 2007 DNA analysis finally revealed that these women (who had been raped before being killed) likely had a com- mon killer. The DNA profile was not in any database. A familial search, done as a last resort in the case, revealed a near match—likely a relative. The relative was too young to have commit- ted the murders, but suspicion focused on his father. Police were able to obtain a surreptitious sample of the father’s DNA from a piece of food he had partially eaten, and it matched. The suspect was identified as Lonnie Franklin Jr. This arrest cleared nine homicides.

There is some controversy around familial searching. Not many people would find fault with what was done in the Grim Sleeper case. But imagine there was a suspect in a major felony case but no probable cause to obtain a search warrant for his DNA. Suppose he had a young son who attended school, and police hung around the school waiting for the child to discard a piece of partially eaten food or a soda can from which he had taken a drink. There is nothing illegal about police collecting such items and running DNA profiles on them. Suppose the DNA profile they obtained was a good enough partial match to convince a judge to issue a search warrant for the father. Some would object to using the child to get to the father, even in this rather anonymous way.

Recently, in 2018 another case in California was solved through familial searching.

Think About It

Do you think that more DNA profiles should be added to the database? If so, whose? If not, why? Under what, if any, circumstances do you think that DNA profiles should be removed?

Section 11.4DNA in Casework

Recently, following the Golden State Killer case publicity, Washington State authorities an- nounced that they had solved a 1987 double homicide case using similar DNA familial search techniques (Green, 2018).

11.4 DNA in Casework Most of the time forensic DNA typing is used in criminal cases and is what has been dis- cussed in the chapter thus far. Evidentiary stains or swabbings are analyzed for DNA profiles.

Case Illustration: Joseph James DeAngelo, the Golden State Killer

The man known variously as the Golden State Rapist and Golden State Killer is thought to have committed more than 50 rapes and 12 murders as well as at least 100 burglaries from 1974 to 1986. Initially based in Sacramento, his crime spree eventually extended to Contra Costa County (in the East Bay Area of San Francisco) and southern California. He is regarded as one of the most prolific serial criminals in the history of the country.

For decades, the cases could not be solved. In 2018 the forensic lab tried something unprec- edented: It took the evidentiary DNA profile and submitted it to a DNA profile website called GEDmatch, which permits comparisons between submitted profiles and others that are already- there. Amazingly, while this strategy did not find an exact match, it found a profile that could have been a relative of the submitted profile’s owner. Through this association, law enforcement was able to focus on Joseph James DeAngelo. DeAngelo had been a police officer in two different departments from 1973 to 1979 but had been fired from the second one for petty criminal activity. To establish their case against him, police seized a specimen of discarded DNA from the door handle of a vehicle DeAngelo had been driving. The specimen profile matched the evidentiary ones from the case. At the time of his arrest, DeAngelo was 72 years old. A newly taken specimen from DeAngelo further confirmed the match.

As of mid-2018, judicial proceedings against him were in the early stages.

Reflect On It The controversy around familial searching of databases has to do with privacy concerns. This case may take that concern a step further, as it was the first example of law enforcement searching a database intended essentially for seeking relatives or ethnicity information. How- ever, the database in question makes it clear that anyone submitting data to it gives up their right to privacy and warns that the data is available to be used for any purpose by anyone.

What do you think about the way law enforcement identified the Golden State Killer?

Associated Press

Section 11.4DNA in Casework

These are then compared with the profiles of known people in the case, or databases are searched to see if they can be found. If there are no known suspects and the profiles cannot be matched in the convicted offender database, the profile may be added to and searched for in the forensic file.

In some states there is a statute of limitations in sexual assault cases. This means that after a certain number of years, the case can no longer be prosecuted, even if a suspect is developed. The advent of DNA typing and databases has opened the door to solving some old cases, often called cold cases. Sometimes the evidence that was collected long before DNA typing became available can be analyzed for DNA. This may result in a profile match in a database, identifying the suspect. Other times the profile cannot be found in a database and is added to the forensic file. However, this effort is of no use if the statute of limitations has run out. In 1999 a creative prosecutor in Wisconsin indicted the owner of a specific DNA profile before the statute of limitations expired, and thus stopped the possibility of prosecution from expiring (Dedman, 1999). If the individual is found, he or she can be tried. A more recent example of this practice took place in Washington, D.C., in 2018 (AP Wire Service, 2018).

The ability to search through databases and identify individuals shows the importance of processing evidence in criminal cases in a timely manner. If a profile is included in a database but the evidence is not processed, the person cannot be identified through a DNA hit. This is one of the issues with lab backlogs. There is a similar issue with older, never analyzed sexual assault evidence collection kits, which in some jurisdictions have numbered in the hundreds. Great progress has been made to process the kits and enter the profiles into CODIS. How- ever, backlogs of current cases remain. If the criteria for databasing profiles increase, such as including all arrestees in the database, without adding necessary resources, the backlogs will increase as well.

DNA can also be used in civil cases. A disputed parentage case is an example. All disputed par- entage cases that are tested in the lab are now subjected to DNA profiling. The profiling will include or exclude a suspected parent, and the probability of parenthood can be calculated. This probability is typically very high for biological parents.

DNA profiling can also be useful in regulatory and other human identity situations, such as in identifying human remains. This is very important for families who need to settle the legal affairs of the deceased. Additionally, DNA typing can be used to prove that a urine specimen found to contain a prohibited drug (Chapter 5.6) actually came from the person whose name is on the label. In other words, DNA may be used to check for a specimen mix- up. This can be very important if someone is facing a major sanction, such as losing a job, because of a drug test.

We have described a “prosecutorial” view of a DNA match in a case. It is important to under- stand that there is also what might be called a “defense” view. When a defense attorney gets a case in which a DNA match associates his or her client with a crime scene or a victim, he or she is thinking about potential innocent explanations for it. One of them is that a relative of the client might be involved. Especially if the profile is not a complete one (i.e., has less than the whole 20 DNA regions because the lab couldn’t type them all), there is the potential for a chance duplicate that is much greater among related people than unrelated people. Another potential issue is laboratory error. Analysts can sometimes make errors. No one wants to see someone wrongfully convicted of a crime because there was a lab error.

Section 11.5Newer DNA Technologies

11.5 Newer DNA Technologies Thus far, Chapter 11 has discussed the typing of nuclear DNA. This is the DNA found in a cell’s nucleus. It replicates before cell division, and a complete copy is passed along to both new cells (daughter cells). Each of us inherits a random half of the DNA from our mother and a random half from our father, by way of a sperm combining with an egg at fertilization. The STR regions that have been discussed are found in this nuclear DNA. There are other types of DNA analysis used in forensic work, including mitochondrial DNA and Y chromosome DNA, that can enable inferences about the person.

Mitochondrial DNA This DNA, which is much smaller in size than the DNA found in the nucleus, is found in cell structures outside the nucleus called mitochondria. Mitochondrial DNA typing is different from nuclear DNA typing. A cell contains several different types of membrane-bound struc- tures in addition to the nucleus. One of them is called a mitochondrion (plural: mitochon- dria). This structure contains the cell’s energy-making machinery. It also contains a small amount of its own DNA, known as mitochondrial DNA (mt-DNA). While nuclear DNA con- tains around 3.5 billion A, T, C, and G units, mt-DNA contains only about 16,000. There are two small regions within mt-DNA that show variation among individuals and ethnic groups. Some of the ATCG letters in the sequence show variation. A list of the ones that do and their position in the sequence is called a mitotype. Over evolutionary time, a number of mitotypes have developed in the human population, and forensic scientists can use them to help iden- tify people. Mt-DNA, unlike nuclear DNA, is inherited only from our mothers. The mitotype is passed from mother to offspring unchanged unless there is a mutation. A mutation is a rare genetic event in which one of the A, T, C, and G letters is converted to a different one or might be deleted from the sequence. Mt-DNA seems to be more robust than nuclear DNA in old, degraded specimens. As a result, it is used by labs trying to identify old human remains and evolutionary biologists studying old bones and ancient human remains. In Chapter 6 we noted that a hair shaft can be a source of mt-DNA. It is also important to recall that if the hair is pulled out (telogen hair), it will have a bulb of cells on its root end, and those cells can be used for nuclear DNA typing, as we have described for blood, body fluids, and tissues.

Cells typically contain from hundreds to thousands of mitochondria (the number depends on the cell type). This means that mt-DNA is present in what we call high copy number. Whereas one cell has one copy of nuclear DNA, it may have 5,000 copies of mt-DNA. From a forensic

Think About It

You worked on creating a partial DNA profile that helped take a suspect to trial. The suspect’s defense attorney states that because only 9 out of the possible 20 DNA regions were typed, the DNA profile is not the suspect’s. The suspect has no known living relatives. Do you believe that the DNA profile could not be the suspect’s? Why or why not? How would you explain your reasoning to the courtroom?

Section 11.5Newer DNA Technologies

standpoint, this is helpful. Not only does it enable scientists to obtain results from small speci- mens, it also means that in old, degraded specimens there is a better chance of finding some mt-DNA intact for analysis.

An mt-DNA match does not individualize a specimen like a nuclear DNA STR match does. The population frequency of a mitotype may be around one person in several thousand. However, mitotyping is not used by itself. Additional information is used to help confirm the identity results. As an example, suppose an American war plane is found in the jungles of Vietnam, and there are human remains on board. These remains can be analyzed by mt-DNA by comparing it with that of a known maternally descended relative. The military keeps records of pilots, so there is strong circumstantial evidence that these are the remains of that person. The mt-DNA match provides additional evidence, and the remains are returned to the family.

Mt-DNA typing is performed in specialized laboratories. It is not a routine technique in every forensic lab. The following are two case examples that illustrate the forensic application of mt-DNA.

Case Illustration: Identification of the Members of the Last Russian Royal Family

During the Russian Revolution of 1917, the monarchy was overthrown. In 1918 in Yekaterinburg, members of the last Russian royal family and members of their household staff were killed, and their remains were thrown into a mine shaft. At the end of the Soviet era in 1991, skeletal remains of the group were exhumed and subjected to forensic examination. Anthropologists identified the tsar, the tsarina, and three of the five children (Tatiana, Maria, and Olga), along with various servants and household staff. The other two children, Anastasia and Alexei, were not in this group.

The case received attention because there were persistent rumors that Alexei and Anastasia had survived. In 1920, after World War I, a woman surfaced in Berlin who claimed to be Anastasia. She later used the name Anna Anderson. She was the most famous claimant to Anastasia’s identity, and some people believed her. She would later live in Charlottesville, Virginia, until her death in 1984.

In 1994 a group led by Dr. Peter Gill of the British Home Office Forensic Science Service ran mt-DNA tests on the skeletal remains of the tsar, his family, and the others who were exhumed in 1991. Figure 11.3 shows how a living maternally derived descendant can be used as a reference specimen for someone long deceased.

(continued on next page)

Photo 12/Universal Images Group/Getty Images The Romanovs, the last Russian royal family.

Section 11.5Newer DNA Technologies

Case Illustration: Identification of the Members of the Last Russian Royal Family (continued)

Figure 11.3: Romanov family trees

Two different family trees are shown. Figure 11.3 shows Princess Alice, a daughter of Queen Victoria of England, at the top. Her mt-DNA passes down through two other women and finally to Prince Philip, Duke of Edinburgh, the husband of Queen Elizabeth II of England. Thus, Philip could be used for the reference sample for the tsarina and for the five children. Similarly, the second family tree is based on a descendant of Louise of Hesse- Cassel and could be used for the reference sample for the tsar. The identities presumptively established by the anthropologists were confirmed by the mt-DNA typing.

This left open the issue of the missing two children and Anna Anderson. Although Anna Anderson had been cremated when she died, there was a biopsy specimen still available from which DNA could be obtained. Mt-DNA analysis was able to show that she was not Princess Anastasia. Detailed investigations, including additional mt-DNA typing, suggest that she was most likely Franziska Schanzkowska.

In 2008 human remains found in the same location as the others but overlooked in the ini- tial exhumation proved to be those of Alexei and probably Anastasia. Anthropological and mt-DNA evidence were used in this case also. It is still unclear whether the remains found with Alexei were those of Anastasia or of Maria. In any event, all the children have now been accounted for and the matter is closed.

This case shows how mt-DNA helped unravel an important historical mystery and identify the members of the last Russian royal family some 80 years after their deaths.

Reflect On It Can you think of any other historical mysteries that mt-DNA could help solve?

Great-great grandson

Great-great-great granddaughter

Louise of Hesse-Cassel

Prince Philip Duke of

Edinburgh

Alice of

Battenburg

AnastasiaOlgaTatianaMariaAlexei

Tsar Nicolas II Tsar Nicolas II

Tsarina Alexandra

Princess Victoria

of Hesse

Princess Alice (second daughter of Queen Victoria)

Grand Duke Ludwig

4th of Hesse

1. 2.

Section 11.5Newer DNA Technologies

Y Chromosome Another newer application of DNA analyzes STRs on the Y chromosome, which is only found in males. This application can aid in sexual assault evidence analysis. Ordinarily, in order to develop a male DNA profile from a mixture of sperm cells and vaginal epithelial cells, which are always present together on a semen-containing vaginal swab, a special type of DNA extrac- tion is used. A clean separation of sperm and epithelial cell (male and female) DNA is usually obtained, but not always. If it isn’t, the DNA is a mixture, and DNA mixture profiles can be dif- ficult to interpret. If analysts were able to look at features found only on the Y chromosome,

Case Illustration: Identification of an Unknown Soldier The U.S. military maintains a site at Arlington National Cemetery in Arlington, Virginia, called the Tomb of the Unknowns. Laid to rest at this site are the remains of soldiers from each war whose identity could not be determined.

The U.S. Department of Defense maintains a laboratory in Maryland called the Armed Forces DNA Identification Laboratory (AFDIL). Its mission, along with that of the Joint Prisoners of War/Missing in Action Accounting Command in Honolulu, Hawaii, is to iden- tify the remains of fallen American soldiers and return them to their families.

The unknown soldier from the Vietnam War was believed to be one of two individuals. The two suspected soldiers had been shot down in 1972 near An Loc, Vietnam, and Lt. Michael J. Blassie’s wallet and identification were found nearby. But initial testing could not confirm whether the remains were his or those of Capt. Rodney Strowbridge.

Michael Blassie’s family felt strongly that the remains might belong to him, and they pressed the Pentagon for the exhumation of his remains and the testing. In 1998 the AFDIL used DNA testing to confirm that the remains were those of Lt. Blassie, and his remains were made available to the family to be interred in the family plot in St. Louis, Missouri. President Bill Clinton personally announced the results of the tests and the identification.

The tomb of the unknowns remains an important place for U.S. service members and for the country. With current DNA and other identification technology having progressed as far as it has, however, there will likely not be any more unknown soldiers to place at the site.

Inscribed on the white marble tomb stone are the words

HERE RESTS IN

HONORED GLORY

AN AMERICAN

SOLDIER

KNOWN BUT TO GOD

Reflect On It Do you think that the government should fund research to improve or find new technology that could help identify human remains, such as those in the Tomb of the Unknowns? Why or why not?

Section 11.6Identification of Human Remains

they would look at strictly male characteristics. For this reason, the idea of Y chromosome profiling is attractive. It can be helpful in cases, but it is not as individualizing as the typi- cal STR profiling, because Y chromosome STRs are not very discriminating in populations— meaning that many men will share the same profile. Y chromosome STR profiling is still con- ducted only in a few specialized labs. Y chromosome STR profiles are not highly individual, but they are useful for excluding men.

Inferring Personal Appearance and Information From DNA A final important point to mention involves taking DNA typing beyond STRs and simple iden- tification and trying to infer a person’s appearance or state of health. As mentioned previ- ously, this is a major concern of privacy advocates. The knowledge and technology have evolved to the point that it may be possible to predict eye color, stature (within some limits), racial origin, and even some general facial features. Law enforcement would argue that this is no different from real-world eyewitness testimony in which someone might say the suspect was “ a White male, about 30 years old, with blue eyes, wearing jeans and a T-shirt.” However, what if it were possible to determine that the person was HIV positive? Or that there was a high probability the person had type 2 diabetes? As a rule, health information like this is pro- tected. But does this protection extend to criminal investigations or investigations of poten- tial terrorists? Apart from DNA analysis, a person’s blood can already be analyzed to see what drugs are present (Chapter 5), whether a person smokes, whether they have been drinking, and so forth. The technology is quickly developing to make it possible to obtain personal information from DNA. In 2018 the Marinette County Sherriff ’s Office in Wisconsin collabo- rated with Parabon NanoLabs to produce composite images and probable features of a sus- pect in an old, cold case. They released the photos to the public and have since received about 30 new tips (WSAW TV, 2018). The debate is ongoing about whether and to what extent such technology should be used in criminal cases, and whether it violates people’s privacy to use their DNA in this way.

11.6 Identification of Human Remains Have you considered how human remains are identified? In places where there are medical examiners, the law requires that they make an effort to identify each body that comes in. Nor- mally, this process is straightforward. There is usually information about who the person is, and the medical examiner then asks someone who knew the person in life to look at the face (or its image) and identify the person.

Think About It

Do you consider providing health information from DNA profiling an invasion of privacy? Would there be any special circumstances under which this type of information would be useful to a case? Suppose it were a terrorism investigation. Do you think law enforcement is entitled to use personal information obtained from DNA to get a lead? What types of informa- tion would be acceptable? Is there anything you would consider off limits?

Section 11.6Identification of Human Remains

However, sometimes bodies are not intact or are badly disfigured or burned. Then what? The next things to analyze are fingerprints and teeth. In these cases the hands must be relatively intact to obtain fingerprints, and the skull must be available with the teeth relatively intact to X-ray the teeth. Fingerprints can be compared with premortem fingerprint records if those records are available within one of the AFIS databases (Chapter 8). If premortem fingerprint records are unavailable, it is impossible to make the identification in this way. Forensic den- tists can X-ray the skull to obtain images of the teeth. These images can then be compared to premortem dental X-rays to make identifications. The challenge is that there are no database files of dental X-rays. In order for this to be successful, investigators must have an idea of who the person might be, and premortem X-rays must be available through the victim’s dentist. Without premortem X-rays, the forensic dentist cannot make an identification.

Let’s say that a body was found with a missing skull and hands. Or maybe it had them, but there were no premortem fingerprint or dental records. At this point, investigators would look at more circumstantial evidence on the body. Scars, marks, or tattoos might be helpful if someone can recognize them or if they fit into a medical history. Even clothing or belongings, like rings, might be helpful.

When the remains are badly decomposed or completely skeletonized, the problem is more difficult. Again, the teeth can be helpful if the skull is available. In these cases a physical (forensic) anthropologist is needed to determine gender, approximate age, approximate stat- ure from long bones, or any trauma or disease that might be helpful in identification.

In the extreme, skulls may sometimes be used by a forensic sculptor to re-create a face. If the person’s racial origin can be inferred by an anthropologist, tissue depth measurements are available to help the sculptor. If any hair remains, hair color might be known. Generally, eye color, hair style, and so forth will be a guess. The idea behind the sculpture is that some- one who knew the person in life might recognize the facial reconstruction and identify the decedent.

In the case of mass disasters, there are many victims, and there is a lot of pres- sure to identify and return them to their families as soon as possible. When such a disaster occurs within the United States, special teams called Disaster Mortuary Operational Response Teams, or DMORTs, are mobilized.

DMORTs consist of mass disaster experts, fingerprint experts, forensic dentists, and other investigators skilled in this type of investigation and trained to work together to collect evidence and identify the remains. Emphasis in these situations is on fingerprints and dental records. The majority of people can usually be iden- tified by one of these means. Airplane crashes are the easiest for the teams

Paul Sancya/Associated Press Using DNA to identify human remains has more than just forensic or anthropological benefits. It also helps return lost victims from mass disasters to their families.

Section 11.6Conclusion

because there is an accurate list of passengers. In train accidents, or when occupied buildings are involved (like the World Trade Center on 9/11 or the Oklahoma City Federal Building in 1995), there is no list of people, so investigators must try to determine who might have been in the building. Certainly, employees might have been in the building, as well as people who run small businesses (like a newspaper stand), people who may have had appointments with businesses in the building, and so on.

Sometimes there is massive damage and fire destruction. This makes locating human remains and identifying them much more difficult. Skulls with teeth and hands with fingerprints are easier to identify than separated fragments of bone or tissue. Faced with the latter, the only option may be DNA profiling. The problem is locating reference specimens. For this, one needs to have an idea of who was there. One type of reference specimen is something directly associ- ated with the person—like a toothbrush. Another approach is using parentage testing meth- ods. This is why family members might be asked to provide specimens for DNA in these situ- ations. The goal is always to identify as many of the human remains as possible and return them to the family.

Conclusion Prior to DNA technology, forensic scientists used blood types and other blood characteristics to partially individualize specimens, but these methods were not very powerful in compari- son to DNA profiling. DNA is the genetic material of all cells and tissues, and it is found in the nucleus of cells. Most body cells have nuclei, except red blood cells.

There are several steps in DNA analysis, including isolation, quantitation, and actual typing. What is actually typed in DNA is the size of a number of small fragments that have been cop- ied millions of times using PCR. PCR enables forensic scientists to analyze very small amounts of evidence. The regions of DNA used for forensic DNA typing consist of tandem repeated segments called short tandem repeats, or STRs. The size of the fragment is proportional to the number of repeats. With today’s technology, the number of repeats can be determined for each locus. DNA is powerful for individualization because there are multiple possible types at every locus, and the population frequencies at all the loci typed can be multiplied, because the types are inherited independently. A DNA profile, even one that includes fewer than the full 20 loci, is highly individual. Probabilities of chance duplication run in the billions to trillions.

DNA types and profiles are sets of numbers that are easily stored in databases. The FBI main- tains the national DNA database called CODIS, which contains records of the DNA profiles

Think About It

You are called to a house destroyed by a homemade bomb. It is suspected that human remains are inside. What type of evidence for identification would you look for? Explain your reasoning.

Conclusion

of convicted offenders, of profiles from cases whose origins are unknown, and from missing persons cases. There are around 11 million profiles in CODIS.

New DNA technologies such as mitochondrial DNA typing and Y chromosome profiling (for males) are being used today. Mt-DNA is inherited from one’s mother and can help identify skeletal remains when there is other circumstantial evidence. Technology development will soon enable inferences about a person’s appearance and/or state of health to be discerned from DNA analysis. There is discussion and debate as to whether such practices would consti- tute unacceptable invasions of privacy.

DNA is powerful technology but tells us only whether a specimen does or does not contain a person’s blood or body fluids. Deciding how to interpret that information in the context of a case requires an inference by the trier of fact. DNA typing does not itself establish guilt or innocence.

There are several methods for identifying human remains, depending on the intactness and condition of the remains. Visual identification of intact bodies is the most common. Dental and fingerprint identifications are the next most common and are often used in mass disaster situations. DNA profiling may be used in the extreme cases to help identify human remains.

Key Ideas

• Blood types and other blood markers were used by forensic scientists in the pre- DNA period to help individualize blood and body fluids and stains. These genetic features did not have the power of DNA typing.

• Using DNA typing to help individualize blood, body fluids, and stains is based on genetics and inheritance in populations. DNA is the genetic material of all cells. DNA typing therefore uses features of the genetic material itself to individualize biological specimens.

• The majority of DNA is found in a cell’s nucleus. This forms the basis of classical inheritance. A small amount of DNA is found in the cell’s mitochondria. It is inherited in a mother-to-offspring manner.

• There are several steps in DNA analysis, including isolation, quantitation, and the actual typing.

• Typing includes making multiple copies of the targeted regions of DNA with poly- merase chain reaction, then analyzing the resulting larger quantity of material.

• Typing itself focuses on 20 DNA regions. These regions contain STR sequences. People differ as to the number of repeats they have on each chromosome. There are multiple possibilities at each region.

• Population studies provide forensic scientists with the frequencies of numbers of repeats in populations needed to compute the probability that a profile will have a duplicate in a population. Population frequencies are ethnic group specific.

• A 20-locus DNA profile has such a small possibility of chance duplication in most populations (of unrelated people) that it is likely to belong only to one individual.

• DNA typing and profiling has applications in criminal as well as in civil and regula- tory cases.

• Mitochondrial and Y chromosome DNA analysis can be helpful in some cases. Not all laboratories perform these analyses.

Conclusion

• A DNA profile in a specimen shows that a person’s DNA was present in the specimen (or its absence can show that it was not present). DNA profiling by itself does not establish guilt or innocence in criminal matters.

• There are several methods for identifying human remains. Some give more certain results than others. The method employed depends on the remains available and their state of decomposition or skeletonization.

Critical-Thinking Questions

1. You may have heard of “cold case” investigative units in police agencies. They go back to old, unsolved cases, review all the facts and evidence, and try to see whether some forensic technique that was not available at the time could help solve the case. If you were looking into a cold case, what would you be looking for that DNA profil- ing could be helpful with?

2. Certain ATCG letter combinations in mitochondrial DNA are indicative of ethnic origin. Keeping in mind that mt-DNA is maternally inherited, how could an investiga- tor be misled by relying on an mt-DNA combination to predict the ethnic origin of a person who left behind biological evidence?

3. In the chapter, we talked about population studies. A population is sampled to figure out the frequencies of DNA types within it. Suppose you worked in Illinois, and you had a DNA match case. The case was going to trial, and you needed to calculate the probability of chance match (as was done in Table 11.1). Looking in the journals, you find population studies for Illinois, Indiana, Iowa, Wisconsin, Michigan, and for a sample of FBI agent recruits from all across the nation. Each of these studies shows different type frequencies. Which one would you pick to use? And how would you justify using one versus another?

4. Suppose you were an investigator, and a severely decomposed set of human remains was found that was missing its head, hands, and feet. What steps could you take to help identify these remains?

5. A woman reports a sexual assault. She is taken to a clinic, and a sexual assault kit is taken. She knows the man she is accusing of the assault and appears to be a com- pletely credible complainant. She tells the police that she has not had sexual rela- tions with anyone for many weeks preceding this incident. The lab receives the sexual assault kit, a known specimen from the complainant, and a known specimen from the suspect. There is semen on the vaginal swab. DNA typing shows, how- ever, that it is not that of the suspect. A CODIS search of the profile does not find anyone. How can these results be explained? Is there any way the suspect could be guilty here?

6. The CODIS database has been expensive to develop and is expensive to maintain. It is helpful to law enforcement when it produces a hit that finds someone who would not otherwise have been found. How might you devise a study to try and figure out the cost effectiveness of CODIS to the general public?

Key Terms buccal Referring to the inside of the cheek. chromosomes Physical structures in the

nucleus of cells that contain and carry DNA. The chromosome number is characteristic for a species. Humans have 46.

Conclusion

deoxyribonucleic acid (DNA) A biochemi- cal that is the structural basis of genetics.

extraction Removal (isolation) of DNA from a stain or fluid.

familial searching Searching a CODIS database for a profile closely related to a questioned profile in the hopes of finding a relative of the profile possessor.

genetics A branch of biology consisting of the study of inheritance.

karyotype The chromosomal makeup of a person. Generally, everyone has 22 pairs of non-sex chromosomes, and XX (women) or XY (men). But some people can have unusual numbers of chromosomes.

locus (plural: loci) Latin for “place.” Refers to a specific region of DNA that is inherited as a unit.

mitochondrial DNA (mt-DNA) The DNA in the mitochondrion.

mitochondrion (plural: mitochondria) A structure within the cell that contains the cell’s energy-producing machinery and a small amount of its own DNA, distinct from nuclear DNA.

mitotype A listing of the ATCG letters at the sites in mt-DNA where there is variation in the human population.

mutation A change in one of the ATCG letters in DNA; for example, a C to a G. The change will be inherited by the next generation.

nuclear DNA The DNA in the cell’s nucleus.

nucleus A membrane-bound structure within the cell that contains its chromo- somes and DNA.

polymerase chain reaction (PCR) A pro- cess by which a small region of DNA is cop- ied many times to produce enough product for easy analysis.

profile A set of DNA types at several loci (regions).

sex chromosomes The X and Y chromo- somes. In many species, including humans, they determine one’s sex. Females are XX, and males are XY.

short tandem repeats (STRs) Head-to-tail repeated sequences of short, core DNA A, T, C, G letter sequences. The STRs chosen for forensic work have core letter sequences of four or five and may be repeated from a few to dozens of times.

typing A DNA type at a locus is the specifi- cation of how many repeats a person has on his or her chromosomes. A person can have the same number on each chromosome (for example, 12,12) or a different number (for example, 12,14).

Web Resources A government website devoted to research on the human genome: https://www.genome.gov

The FBI Laboratory website, containing the CODIS section: https://www.fbi.gov/services/laboratory

The Arlington Cemetery website, Vietnam unknown section: http://www.arlingtoncemetery.net/vietnam.htm

Conclusion

The Arlington Cemetery website, Tomb of the Unknowns section: http://www.arlingtoncemetery.net/tombofun.htm

The website of the Disaster Mortuary Operational Response Teams: https://www.phe.gov/Preparedness/responders/ndms/ndms-teams/Pages/dmort.aspx

A website with extensive legal and legislative information about DNA in a forensic context: http://www.dnaresource.com

Audio from NPR news stories on DNA database use by law enforcement: https://www.npr.org/series/17128722/the-ethics-of-dna-use