Forensic Genealogy: How In-Home DNA Tests Can Help Law Enforcement

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Forensic genealogy is the newest member of the forensic family—and its ability to match people to evidence could be as revolutionary to investigations as the use of fingerprint analysis was.

Since cracking its first case in 2018, forensic genealogy has helped identify suspects in dozens of cases of murder and sexual assault. By the middle of 2019, one forensic genealogy lab claimed to be solving cold cases at the rate of one per week. But regulators, citizens, and even forensic genealogists themselves are concerned with the practice’s implications for privacy and jurisprudence.

Forensic genealogists use genetic information to match individuals to DNA samples. This often means utilizing open-source databases, such as GEDMatch. While GEDMatch does not offer genetic testing itself, it does allow the upload and comparison of DNA data from third parties, including direct-to-consumers services such as or 23andMe. GEDMatch holds the genetic profiles of over 1.2 million individuals, which is enough to identify a third cousin (or closer) of a DNA sample in 90 percent of the US population. Law enforcement can then use this capability to begin building a family tree of a suspect and/or victim, aided by public records and traditional sleuthing.

Case Example: Catching the Golden State Killer

The first person that forensic genealogy put behind bars was a former police officer named Joseph James DeAngelo. As the Golden State Killer, he terrorized Californians off and on from 1973 to 1986: 13 murders, 50 rapes, and 120 burglaries. His identity eluded law enforcement for decades.

In 2018, investigators pulled the Golden State Killer’s DNA from a rape kit and uploaded it to GEDMatch. In return, they received over a dozen people who had the same great-great-great-grandparents as the killer. Working with a genealogist, the investigators began constructing a large family tree, ultimately narrowing their search to two possible suspects. When a follow-up DNA test ruled out one of those two, the investigators had their prime suspect: Joseph James DeAngelo.

After collecting a sample of DeAngelo’s DNA from his car door handle and another from a tissue he discarded, the team of investigators and genealogists ran further tests and found that these samples matched DNA collected from the crime scenes of the Golden State Killer. DeAngelo was arrested on April 24, 2018, and was eventually sentenced to multiple consecutive life sentences, with no possibility of parole.

The Controversy Surrounding Forensic Genealogy

Forensic genealogy is the most powerful tool that investigators have gained in the 21st century, but its quick adoption and lack of oversight have led to some serious debates around privacy and due process.

Most forensic genealogy investigations are performed without a warrant, yet they search through millions of people’s records to access extremely sensitive personal health information about an individual—information that has not been explicitly volunteered. Websites and tools that were originally meant to help people discover their ancestry are now being utilized by investigators in a way that may violate a citizen’s Fourth Amendment rights.

Before it cracked the Golden State Killer case, forensic genealogy didn’t really exist. Afterward, however, every genetic database and DNA testing site was looked at as a potential forensic genealogy outfit. Requests from law enforcement came pouring in and some genealogy databases, such as FamilyTreeDNA, quietly changed their terms and conditions to accommodate those requests without upsetting users.

While major players like Ancestry and 23andMe resisted collaboration with law enforcement, others saw an opportunity to make themselves a niche within the market. FamilyTreeDNA continued its push, releasing ads encouraging people to upload their DNA to help solve cold cases, simultaneously jacking up pricing for law enforcement queries by 700 percent.

In response to the controversy, GEDMatch updated its policies such that users must opt-in for law enforcement to be able to use their information for investigative purposes. Approximately 20 percent of its users have done so. But in the interim, the database has made exceptions, without oversight, for personal requests from law enforcement. In December 2019, GEDMatch was acquired by a genetic sequencing company dedicated purely to forensics.

While the industry charges ahead, cracks have appeared in forensic genealogy’s armor. Forensic genealogy has helped to solve cold cases, but it’s also accused innocent people. Ancestry tests can be misinterpreted, and direct-to-consumer testing data can be flawed. And, most worryingly, no exams or credentials yet exist for forensic genealogy.

The Future of Forensic Genealogy

In September 2019, the US Department of Justice issued guidance that stated federal investigators should only use forensic genealogy in cases of murder and rape or to identify human remains—and only as a last resort. It was the first statement of policy around the practice of genetic-genealogy matching as an investigative tool. But, crucially, the guidelines did not apply to state and local law enforcement, who perform the bulk of the nation’s investigations.

States and municipalities are currently fighting it out to introduce their own legislation. Utah has introduced a bill that would ban genetic searches by law enforcement, while New York has proposed a policy that would allow them. Washington state has split the difference and suggested they should only be an option when requested through valid legal processes. This patchwork of conflicting guidance may not amount to much more than confusion in a world where cases, and families, often cross state lines.

A 2019 survey by Pew Research Center found that 48 percent of Americans thought it acceptable for DNA testing companies to share customers’ genetic data with law enforcement. But with up to 90 percent of the country potentially identifiable through forensic genealogy, that’s a lot of Americans being searched without consent.

The American Journal of Human Genetics recently published the largest-ever international survey on genomics and found that less than half of 36,000 respondents were willing to share their DNA for research and medical purposes, citing a lack of trust. Governmental regulations, investigative rigor, and corporate oversight of forensic genealogy outfits are required to help restore part of that trust.

Forensic genealogy has achieved a remarkable amount for how young it is, and many of its flaws are the product of its rapid ascent to the mainstream. The allure of solving cold cases and bringing justice to those who thought it lost may be too great to reign in the power of forensic genealogy. But as the field grows into itself with formal education, accredited certification, and peer-reviewed research, it can begin to live up to the rigorous standards of other investigative disciplines.


Matt Zbrog

Matt Zbrog is a writer and researcher from Southern California. Since 2018, he’s written extensively about the increasing digitization of investigations, the growing importance of forensic science, and emerging areas of investigative practice like open source intelligence (OSINT) and blockchain forensics. His writing and research are focused on learning from those who know the subject best, including leaders and subject matter specialists from the Association of Certified Fraud Examiners (ACFE) and the American Academy of Forensic Science (AAFS). As part of the Big Employers in Forensics series, Matt has conducted detailed interviews with forensic experts at the ATF, DEA, FBI, and NCIS.