How Is DNA Profiling Used to Solve Crimes?

DNA profiling is a state-of-the-art procedure that can be used to identify individuals on the basis of their unique genetic makeup. While people may share the same eye and hair color, and may even have similar facial features, they will not have the same DNA. This means the process can be useful in more accurately solving crimes. Forensic scientists can compare DNA found at a crime scene (from blood or hair, for example) to DNA samples taken from suspects. If there is no match, they may be able to rule out that suspect. If there is a match, police will likely want to take a closer look.

Such technology has revolutionized the criminal justice system over the past decades, increasing the likelihood of identifying criminals with virtual certainty. This can make it not only easier to identify perpetrators, but just as importantly decreases the odds of mistakenly putting innocent people behind bars.

In some cases, advances in DNA profiling have allowed law enforcement professionals to solve decades-old cases based on samples of DNA-rich material (such as fingernail clippings) collected before DNA testing was possible.

In other cases, a DNA profile may have been created at the time of the crime, but no match was found during the initial criminal investigation. This problem is now easier to overcome thanks to current database technology, which allows for DNA profiles to be stored and quickly searched. Alternately, DNA profiling advances have also enabled law enforcement to exonerate people who were wrongfully convicted of crimes they didn’t commit.

The road to modern DNA profiling has been long, and it has taken forensic scientists decades of work and fine tuning to develop the highly accurate testing and analysis procedures available today. This article examines how current methods for DNA profiling came to be, and explains the procedure’s current role in the contemporary criminal justice system, including its risks and benefits.

While DNA is one important factor in solving crimes, it is not the only one. Other aspects of criminal investigation — such as forensic psychology — remain an integral part of the process when it comes to capturing offenders. We’ll also explore the role of forensic psychologists, their impact on criminal justice, and the profession’s career outlook.

Before diving into the details of DNA profiling, it’s important to understand what DNA is. Each person has unique DNA, an acronym that stands for deoxyribonucleic acid — the essential building block of the body’s cells. DNA is made up of four chemical bases: adenine (A), guanine (G), cytosine (C), and thymine (T). How these DNA bases are sequenced and organized in an organism’s genome, a kind of genetic blueprint, provides cells with the information needed to build an organism.

Each cell in the body has a nucleus, an inner core, which holds chromosomes. DNA molecules make up these chromosomes. The chromosome contains “markers” — points that repeat short DNA sequences again and again. Just how many times a sequence repeats at each marker varies depending on the person. Every person has two copies — called alleles — of each marker: one from the mother’s side and another from the father’s. Forensic scientists can use so-called short tandem repeats (STRs) of DNA to identify individuals.

Because DNA is hereditary, DNA testing is often used in legal cases to determine maternity or paternity — for instance, when child custody and child support issues are at stake. As the U.K. National Health Service explains, scientists can compare the DNA of two persons using a blood test or even a saliva swab taken from the inside of the cheek. DNA testing can even be performed before a child is born, using tissue taken from the placenta or a sample of the amniotic fluid surrounding the child in the womb. This type of test can also be used to check for genetic abnormalities indicative of illnesses and diseases.

DNA is not just a unique personal identifier, but it can also reveal details about a person’s heritage. Advances in DNA technology have allowed for the surge of at-home genealogy kits that provide people with information about their possible genetic background. Companies like 23andMe and Ancestry.com sell do-it-yourself DNA kits, which are delivered to the consumer’s front door. The person provides a saliva sample and sends it back to the company, which analyzes the individual’s ancestry.

For instance, a consumer DNA kit might identify a person’s DNA shares key components with traditionally West African DNA, as the Live Science article “How Do DNA Ancestry Tests Really Work?” explains. The rise of DNA-driven genealogy databases is also one trend that has supported the increased use of DNA profiling in the criminal justice system.

The first step in DNA profiling is to procure relevant DNA samples. Only a small number of cells from a person’s skin or the root of a hair — or from bodily fluids like blood, saliva, or semen — is needed to build a unique DNA profile. DNA is often discovered at crime scenes during police investigations, after which persons of interest may be asked to voluntarily provide their DNA sample. If there is a strong body of evidence against a suspect, the courts can order them to provide a DNA sample.

Once forensic scientists obtain a sample, they extract the DNA from cells in bodily fluids or tissues and copy it. They then separate the copied markers using a process known as capillary electrophoresis. This enables them to identify distinct markers and the number of repeats for different markers in each allele. The forensic scientists read this data using a chart called an electropherogram, which plots fragments of DNA and shows how many repeats there are for each marker and where they occur. Based on this chart, forensic scientists generate a DNA profiling definition that law enforcement professionals can read. This definition consists of a simple list of numbers, indicating how many repeat units are in each allele of 20 marker points throughout the person’s genome.

The first recognized case of DNA profiling in the forensic science community was that of Colin Pitchfork. In 1986, a girl named Dawn Ashworth was sexually assaulted and murdered in Leicester, England. A man named Richard Buckland confessed to the crime, but police were not confident that he was the killer. They approached Alec Jeffreys, a genetics professor at the University of Leicester, for help. Jeffreys had previously discovered that each person’s DNA exhibited distinct patterns that could be used to distinguish one person’s DNA from another’s. Jeffreys compared DNA from the crime to Buckland’s, and as police had suspected, it did not match.

Jeffreys went on to analyze over 4,000 DNA samples voluntarily provided by men in the Leicester area who wanted to clear their names and help find the perpetrator. Still, no match was found. Then one man confessed that he had been paid to provide a false sample on behalf of the actual perpetrator — a man named Colin Pitchfork. When Pitchfork’s DNA was checked, it matched the DNA at the crime scene. He was sentenced to life in prison in January of 1988.

DNA profiling can also be used to exonerate the wrongfully convicted. For instance, 70-year-old Craig Coley was freed from a California prison in 2017 after DNA testing cleared him of a double-murder he had been convicted of 1978.

Coley had been sentenced to life in prison without parole. Throughout his trial and afterward, he had always maintained his innocence. When biological samples from the crime scene were retested in 2015, the results showed the DNA at the crime scene did not match Coley’s — and that other people’s DNA was present. According to area police, the technology for testing the crime scene DNA sample wasn’t available in the 1970s when Coley was convicted. Reuters reports that Coley is one of more than 350 people exonerated in the U.S since 1989 thanks to DNA testing.

It has taken forensic scientists years to develop the highly accurate testing procedures that make examples like those above possible. Today’s processes rely on the aforementioned STRs, short tandem repeats. A single STR used in today’s forensics is some three to five DNA bases in length. In the past, much longer repeat segments of bases were required, measuring from hundreds to even tens of thousands. Also in the past, when DNA was isolated and separated into fragments, it was labeled using radioactive phosphorus and then examined using X-ray-sensitive film. The entire process took anywhere from six to eight weeks.

Today, the process is more streamlined thanks to the switch to STRs. Another advance that has made DNA profiling more efficient is the transition from gel electrophoresis to capillary electrophoresis to separate DNA. Gel electrophoresis can’t withstand electric fields of more than 40V, while capillary electrophoresis can apply voltages of up to 30,000V, reducing separation time to mere minutes instead of hours.

Additionally, DNA analysis has advanced greatly due to the development of a technique known as polymerase chain reaction, or PCR. This process involves heating and cooling DNA samples in cycles, ultimately “amplifying” the DNA and making fragments easier to detect. With this development (which was ultimately recognized with a Nobel Prize, a landmark moment in DNA profiling history) forensic scientists are able to work with smaller amounts of biological evidence.

Previously, a bloodstain for example, would have to be at least the size of a dime or quarter to elicit enough DNA for a profile. With PCR, profiling is possible with even smaller amounts of blood. Today’s DNA profiling is more sensitive. As a result, investigators can often retrieve DNA from minute numbers of skin cells left behind by a criminal. They can even distinguish the DNA of multiple individuals (for instance, if many people touched the same surface).

Such advances in the technologies and processes used to collect and analyze DNA are just part of what makes advanced DNA profiling so useful. Another aspect is the rise of database technology. When law enforcement professionals can comb through large volumes of DNA data stored in computer databases, they have better odds of finding matches for material collected at crime scenes.

The Federal Bureau of Investigation (FBI), for example, relies on the Combined DNA Index System, or CODIS, which uses computer and DNA technologies to compare DNA profiles. It can generate investigative leads in scenarios where biological evidence, such as semen or blood, has been recovered from a crime scene. Each CODIS profile has a specimen identifier, the processing lab’s identifier, and the actual DNA profile. Law enforcement in different jurisdictions can use CODIS to coordinate distinct investigations and share leads. Matches generated via CODIS allow law enforcement to pinpoint a suspect’s identity.

In recent years, the criminal justice system has also turned to other types of databases — genealogy databases — to identify suspects. As mentioned before, private companies sell at-home DNA testing kits, which people can use to discover more about their genetic history. These companies often encourage users to upload their data for genealogical purposes. This enables them to more readily identify connections, even putting them in touch with distant relations.

In Spain, a woman who was taken from her biological parents as a baby under the Franco dictatorship found her biological family through such a DNA database. In some cases, police can also comb through these files for DNA profiling purposes, searching for individuals who may be criminal suspects or related to suspects.

In 2019, for instance, a 35-year-old cold case murder in Wisconsin was solved using DNA and genealogy databases. Following the 1984 rape and murder of a woman in Milwaukee, police were able to compose a DNA profile of the perpetrator based on semen found at the crime scene. There was no known suspect at the time, however, so police were unable to find a match for the sample. Decades later, police began searching through genealogy databases, which hold millions of DNA profiles, thinking they might find someone who was related to the perpetrator. They identified one individual who turned out to be the killer’s second cousin. Through this family connection, they were able to trace the family tree and find the killer, whose DNA was a match with the sample collected from the crime scene over 30 years prior.

These examples highlight some of the primary uses of DNA profiling in today’s legal system. The process can be used to identify potential suspects and link suspects to a crime, proving they were at a certain place. DNA profiling also enhances the criminal system’s accuracy. Eyewitness accounts are unreliable, particularly in high-pressure situations during the commission of a crime. In the article “The Neuroscience of Memory: Implications for the Courtroom,” researchers note that memory distortions can cast doubt on eyewitness testimony. By comparison, DNA is scientifically accurate and thus more difficult to dispute.

It’s clear that advances in DNA collection and analysis, combined with the power of DNA technology, have in many ways transformed the criminal justice system. However, it’s important to note that although DNA profiling is highly accurate and can play a big role in catching criminals, it’s only one part of the overall criminal justice process.

It takes more than DNA to convict a person of a crime. Forensic psychology remains an integral part of the process, for example. This application of psychology in the legal field is central to deepening law enforcement’s understanding of criminal behavior. Forensic psychologists can help answer questions such as who committed a crime and why. It can also help discern why a person committed a crime in a certain manner — for instance, by opting for a particular weapon. Forensic psychologists also deal with the impact of crimes on victims and may work in victim advocacy.

Although DNA profiling undoubtedly has many practical uses, there are some drawbacks. Questions have already been raised about the ethical implications of catching criminals based on searches of their family’s DNA (as exemplified in the Wisconsin case noted earlier). Nature, the weekly scientific magazine, highlights a number of such instances and the fact that most people who use genealogy databases are unaware that law enforcement may be able to subpoena their information.

There are also ethical and privacy concerns when it comes to law enforcement storing DNA data from convicted criminals. Storing an individual’s DNA, even if they have been convicted of a crime, can be seen as a violation of a basic human right to privacy.

The MIT Technology Review even goes so far as to call large-scale databases like those used to find the Golden State Killer a “national security leak waiting to happen.” Unlike a credit card, which can be replaced, a person’s genome can’t be. The article argues that foreign intelligence could grab millions of American DNA profiles from a database and potentially use the information to identify the true identities of American diplomats or spies and their relatives. They could also pinpoint political information that could potentially be compromising. While this has yet to happen as far as we know, the possibility is very real. The technology is there, and so is the data.

Another concern with DNA profiling is the procedure itself. Although very accurate, it is not 100% foolproof. A partial DNA profile (one that is not complete), for example, may match with multiple people and should not serve as conclusive evidence.

DNA can also be abused, misused, or misunderstood, causing miscarriages of justice. In 2011, a careless lab error resulted in an innocent man being charged with rape because his DNA was erroneously found to match a sperm sample taken from the victim. It later became clear that the lab had mixed up its files. In short, DNA is just one piece of the criminal justice puzzle, and should not be relied on to the exclusion of other investigative and analytical tools.

The cutting-edge science of DNA profiling requires professionals to work in laboratory settings that are removed from evidence collection and apart from the human element of criminal justice. While their work is an integral part of the modern criminal justice system, many who are interested in justice-related careers may be drawn to other specialties.

Consider forensic psychology, which provides the opportunity to examine crime as it relates to the human psyche in the cases of both perpetrators and victims. Those in the field may work to pinpoint future indicators of violent behavior, for example, or help victims through advocacy support. As a career, psychology as a whole is a growing field, with the U.S. Bureau of Labor Statistics (BLS) predicting a growth rate of 14% between 2018 and 2028.

Individuals who are interested in learning more about forensic psychology would do well to explore Maryville University’s online BA in Forensic Psychology. The program covers both psychology core curricula, from social psychology to cognition, as well as criminal justice coursework covering everything from juvenile delinquency to multicultural issues. Students are further encouraged to gain practical experience through an internship, enabling them to understand the connection between course material and its real-world application.

This Maryville University online BA offers a comprehensive mixture of both theoretical and practical teaching. This approach is designed to prepare students for rewarding careers in a number of roles — in police departments or medical laboratories, working with parolees and probation offices, excelling as victim advocates, and beyond. The curriculum also provides a strong foundation for those interested in pursuing further education to become forensic psychologists.
If you’re drawn to a career in criminal justice that performs beyond the lab — and takes into account the human condition — explore Maryville University’s online BA in Forensic Psychology program today.

Recommended Reading

BA Forensic Psychology Careers

How to Become a Forensic Psychologist

An Introduction to the World of Forensic Psychology

Sources

Chemical and Engineering News, “Thirty Years of DNA Forensics: How DNA Has Revolutionized Criminal Investigations”

The Guardian, “DNA Database Helps one of Spain’s ‘Stolen Babies’ Find Family”

Investigative Genetics, “DNA Fingerprinting in Forensics: Past, Present, Future”

JSTOR Daily, “How Forensic DNA Evidence Can Lead to Wrongful Convictions”

Live Science, “How Do DNA Ancestry Tests Really Work?”

The Malaysian Journal of Medical Sciences, “Forensic DNA Profiling and Database”

MIT Technology Review, “The DNA Database Used to Find the Golden State Killer Is a National Security Leak Waiting to Happen”

National Review of Neuroscience, “The Neuroscience of Memory: Implications for the Courtroom”

Nature, “The Ethics of Catching Criminals Using Their Family’s DNA”

NBC News, “35-Year-Old Cold Case Murder in Wisconsin Solved Using DNA and Genealogy”

Reuters, “After DNA Test, California Man Freed From Prison in 1978 Double-Murder”

The U.S. Bureau of Labor Statistics Occupational Outlook Handbook, “Psychologists”

U.K. National Health Service, “What Is a Prenatal Paternity Test?”

U.S. National Library of Medicine, What Is a Chromosome?”

U.S. National Library of Medicine, “What Is DNA?”