Personal Genetics Education Project

Genetics, law enforcement and crime

The collection and analysis of DNA is an important tool in law enforcement. According to the FBI, as of 2018, almost 400,000 cases have used DNA evidence to aid in criminal investigations. In addition, the Innocence Project states that over 350 people, several of whom were on death row, have been exonerated as a result of DNA evidence. As of 2018, over 16 million people in the United States have their DNA profile in a criminal offender or arrestee database, more than two-thirds of which were added in the past ten years. Some expect this number will continue to climb as a result of the 2013 Supreme Court decision in Maryland v. King, in which the Court ruled to allow law enforcement to collect DNA from people who are arrested, but not charged or convicted of a crime. As of 2018, all states and Puerto Rico collect DNA from individuals convicted of at least some felonies, and 40 states also collect DNA from those convicted of at least some misdemeanor charges. 30 states and Puerto Rico collect DNA from individuals arrested, but not convicted, of certain crimes. For arrestees who subsequently are not charged or are acquitted, their DNA data may be expunged automatically (in a few states such as Illinois, Maryland and Texas) or upon request by the individual.

(For an exploration of the science behind forensic DNA analysis, see here.)

DNA as evidence – How do we balance public safety, privacy, and civil rights?

Two cases serve to highlight the challenge of establishing ethical and legal frameworks in a timely manner to guide the use of newly developed technologies. The key to solving both of these cases came from the identification of a partial match between DNA found at the crime scene and DNA from a biological relative of the person who committed the crime.

Between 1974 and 2004, Dennis Rader murdered 10 women. Police had evidence to strongly suspect Rader, but not enough to make an arrest. They subpoenaed his daughter’s medical records and, as a result, obtained her DNA from a sample taken during a pap smear, a common gynecological test for women. If the daughter’s DNA were closely related to DNA from the crime scene, the police would have enough evidence to make an arrest. This is exactly what happened and, when confronted, Rader confessed to the murders. Captured and convicted in 2005, he is serving 10 consecutive life sentences.

In the second case, a man named Darryl Hunt was freed thanks to DNA analysis, after spending 19 years in jail for a crime he did not commit. Using an approach known as “familial searching,” investigators deliberately searched criminal databases for a partial match to DNA found at the crime scene and, as a result, were able to link the crime to the brother of a man whose DNA profile was already in the database.

As of 2018, 11 states, including California, Texas and New York, have official protocols for familial DNA searching, and law enforcement in other states such as Massachusetts have also made use of the technique. On the other hand, Maryland and Washington DC had formally prohibited the use of familial DNA searching.

There are a number of controversies surrounding the use of DNA to solve crimes, from both technical and social perspectives. Human errors can make its way into the forensics procedure. DNA from crime scenes may also be limited in amount, of poor quality, and a mixture of many individuals’ genetic material. The complexity of using such DNA to find matches in DNA databases may lead to erroneous interpretation of the evidence, especially when only partial matches come up, or when doing familial searches. DNA of one person may also be transferred via a third party to the crime scene or victim. Moreover, it has been estimated that African Americans comprise approximately 40% of FBI’s CODIS (Combined DNA Index System) database, despite making up about 13% of the United States population. This raises the concern that relatives of African-Americans are more likely to be identified in familial searches of an offender database.

In an important recent development, journalists discovered in 2015 that law enforcement agencies have been seeking information from the DNA databases of consumer genetics companies, to whom millions of people have submitted their DNA samples for health or ancestry testing. Companies such as 23andMe and AncestryDNA have since disclosed that, if presented with a court-issued warrant, the companies would evaluate the requests on a case-by-case basis, and share a customer’s DNA information with the police if compelled by law.

The key question is how we as a society can use genetics to keep people safe, solve crimes and, at the same time, develop policies that ensure fairness and provide appropriate safeguards and privacy protections. Many experts or the broader public do not agree on how DNA should be used to prevent and solve crime, and the issue will likely be the subject of many legal debates and court cases for years to come. In April 2018, it emerged that police in California made use of familial searching and a public database, where genealogy enthusiasts and researchers upload and share DNA data, to arrest a suspected serial rapist-and-killer. This has raised further questions and debate about the balance between public safety and privacy.

Is there a “violence gene”?

The idea that “crime runs in families” is deep-seated, and the claim that heredity analysis and reproduction controls can be used to get rid of “undesirable” personality or social characteristics from our population formed the basis of the eugenics movement in the early 20th century. But questions about whether genetics can, in part, explain violent, aggressive behavior in humans remain highly debated today.

Media coverage of recent episodes of extreme violence in the United States and elsewhere is bringing a renewed focus on how genetics might impact criminal behaviors. For example, following the killings in Newtown, Connecticut, the state medical examiner’s office asked for an analysis of the DNA of the gunman, Adam Lanza. This was covered by a number of news sources, including the New York Times that featured an article entitled “Seeking Answers in Genome of Gunman.” Headlines such as this raise the question: “Why study his DNA?”

In trying to tackle the genetic underpinning of complex human behavior such as violence and aggression, it is important to keep a number of concepts in mind:

Genetic complexity: In general, there is not a simple relationship between our genes and our traits. Our physical, mental and behavioral states are the result of complex interactions between multiple genes in combination with our environment and our lifestyles. For example, height is influenced by the action of at least 180 regions in one’s genome in addition to environmental factors, including diet as well as maternal and childhood health.

Biological determinism: This is a framework for understanding humans through a biological lens and aims to explain complex human traits as being largely, if not entirely, dictated by biology, particularly our genes. The concept of biological determinism downgrades, if not dismisses, the role that culture and environment might have in shaping human behaviors. There has been much criticism of this idea, and many scientists are now focusing also on interactions between genes and environment and how that relationship may impact traits and behaviors.

Population genetics: Genetics research seeks to make connections between people’s genetic make-up and their traits. Often, the relationship is not a simple one, but rather a statistical correlation based on what percentage of people in the population with a shared genetic make-up exhibit a particular trait. Your DNA sequence can inform you about your predisposition for certain traits, such as your likelihood for reaching a certain height or your risk for developing a disease. It is important to note, however, that predispositions are not guarantees.

To date, there is no genetic variant that has been perfectly correlated with aggressive behavior. Even for variants that some researchers have correlated with aggressive behavior, there is much controversy. It is important to note that correlations are statistical descriptions of populations consisting of many people and, therefore, cannot be used to determine whether or not a given individual will exhibit aggressive behavior.

Grappling with the genetic basis of aggression will have significant real-world implications. Already, some judges and jurors have reduced sentencing for convicted criminals based on the presence of genetic variants that, in combination with childhood environment, are purported to lead to increased aggressive behavior. At the same time, the possibility has been raised of using an individual’s genetic makeup to predict his or her likelihood of committing crime.

As the cost of genetic analysis continues to drop, and the technologies become increasingly available to a broader population, it is likely that there are many useful or interesting things a person might learn from a personal genome sequence. However, the path to truly understanding the utility and limits of this information will be a lengthy and sometimes confusing one. This is particularly true when it comes to seeking genetic explanations not just for complex human disease and traits, but also behaviors that must be understood in the context of environment, culture and society.

Read more:

Nicola Davis, “DNA in the dock: how flawed techniques send innocent people to prison” (The Guardian, October 2017)

The DNA of a Killer” (48 Hours on CBS, April 2017)

Katie Worth, “The Surprisingly Imperfect Science of DNA Testing” (The Marshall Project, June 2015)

Andrew Pollack, “Building a Face, and a Case, on DNA” (New York Times, February 2015)

Nathaniel Comfort, “Could Genetics Help Us Understand Mass Killers?” (Hartford Courant, January 2013)

John Lauerman, “DNA of Newtown Gunman Unlikely to Yield Clues of Violence” (Bloomberg, December 2012)

Ellen Nakashima, “From DNA of Family, a Tool to Make Arrests” (Washington Post, April 2008)


Related blogposts:

Brianna’s Law has matched more than 1,000 arrestee DNA samples to crimes” (January 2018)

In the news: DNA and the criminal justice system” (April 2015)


Related lesson plans:

DNA, crime and law enforcement

800px-Supreme_Court_US_2010The collection and analysis of DNA is an important tool in law enforcement. This lesson explores the challenge of establishing ethical and legal frameworks in a timely manner to guide the use of newly developed technologies. A key question that is woven through this lesson is how we as a society can use genetics to keep people safe, solve crimes and, at the same time, develop policies that provide appropriate safeguards and privacy protections.

Download lesson plan: Word document or PDF
Download slideshow: PowerPoint slides

Genes, environment and genetic complexity: Aggression in humans

2015-Dana-brainQuestions about whether genetics can, in part, explain violent, aggressive behavior in humans are not new. Recent episodes of large-scale violence, whether in schools or other public places, have renewed discussion about the intersection of crime, mental health and genetics. In this lesson, students are asked to examine popular but incorrect ideas related to the idea that a single gene or even set of genes can “cause” humans to behave aggressively.

Download lesson plan: Word document or PDF
Download slideshow: PowerPoint slides