Forensic Genealogy: When Family History Meets Criminal Justice

In April 2018, California investigators announced the arrest of Joseph James DeAngelo, the man known as the Golden State Killer — a serial murderer and rapist who had evaded justice for more than four decades. The breakthrough did not come from a fingerprint, a witness, or a surveillance camera. It came from genealogy.

Investigators uploaded DNA from a crime scene to GEDmatch, a public genealogy database, and identified distant cousins of the suspect. Working with forensic genealogist Barbara Rae-Venter, they built out family trees from those matches, narrowed the pool of candidates using age and geography, and ultimately identified DeAngelo. The arrest sent shockwaves through both the law enforcement and genealogy communities — and forever changed how the world understood the power of family history research.

What Is Forensic Genealogy?

Forensic genealogy is the application of genealogical research methods and genetic genealogy tools to legal investigations. It encompasses two primary areas: identifying unknown individuals (such as unidentified remains or anonymous suspects) and verifying identity claims in legal proceedings such as estate cases, immigration hearings, and paternity disputes.

The discipline has existed in some form for decades — genealogists have long assisted courts with inheritance cases and identity verification. But the explosion of consumer DNA databases in the 2010s created an entirely new frontier. When millions of people voluntarily submitted their DNA for ancestry testing, they inadvertently created a vast investigative resource. Because DNA is inherited, a criminal who has never taken a DNA test may still appear in a database through the genetic profiles of cousins, siblings, or other relatives who have.

How Investigative Genetic Genealogy Works

The process typically begins with DNA recovered from a crime scene or from unidentified human remains. This DNA is uploaded to a public genealogy database — most commonly GEDmatch or FamilyTreeDNA, both of which allow law enforcement uploads under specific consent policies established after 2019.

Investigators then identify database matches — people who share segments of DNA with the unknown individual. These matches are typically distant relatives: third cousins, fourth cousins, or further. From these starting points, forensic genealogists build extensive family trees, working both backward through time to find common ancestors and forward to identify all living descendants of those ancestors.

Using additional filtering criteria — geographic location, age, sex, and physical characteristics — the pool of candidates is progressively narrowed. When a likely suspect is identified, investigators typically obtain a DNA sample from that person (from a discarded item such as a coffee cup or cigarette) to confirm the match before making an arrest.

The Cases That Defined the Field

The Golden State Killer case brought forensic genealogy into public consciousness, but investigators have since applied the technique to hundreds of cases across the United States. Cold cases that sat unsolved for thirty, forty, and even fifty years have been closed using these methods.

Perhaps equally powerful is the use of forensic genealogy to identify unknown victims. The DNA Doe Project, a volunteer organization of forensic genealogists, works exclusively to identify unidentified human remains using genetic genealogy. Since its founding in 2017, the project has given names to dozens of individuals who might otherwise have remained anonymous in death — returning them to their families and providing long-awaited closure.

Forensic genealogy has also played a role in exoneration. When DNA evidence excludes a convicted individual, genetic genealogy can sometimes identify the actual perpetrator, helping to free the wrongly imprisoned while bringing the true offender to justice.

The Ethics and Privacy Debate

The power of forensic genealogy has also generated significant controversy. When a person submits a DNA sample to a consumer testing company, they are making a personal choice about sharing their own genetic information. But their DNA also contains information about relatives who never consented to any testing. When law enforcement accesses genealogy databases, every person with a profile in that database becomes a potential investigative lead — regardless of whether they have any connection to a crime.

Privacy advocates have raised serious concerns about this dynamic. In response, major genealogy platforms have updated their policies. AncestryDNA and 23andMe do not permit law enforcement uploads. GEDmatch revised its terms of service in 2019 to require users to actively opt in to law enforcement matching, rather than being included by default. FamilyTreeDNA allows law enforcement uploads under a specific program with defined guidelines.

The forensic genealogy community has also developed its own ethical standards. The Forensic Genealogy Institute and various professional organizations have established guidelines emphasizing that the technique should be reserved for serious violent crimes, that privacy should be protected wherever possible, and that findings should always be confirmed by traditional DNA testing before any legal action is taken.

Forensic Genealogy and Family History Research

For those of us in the genealogy community, forensic genealogy represents both a remarkable validation of our discipline and a reminder of its profound responsibilities. The tools and techniques that family historians use every day — building trees from DNA matches, tracing descendants, evaluating documentary evidence — are the same tools that investigators use to solve the most serious crimes.

This intersection carries important lessons. The DNA profiles we upload and the family trees we build are not merely personal records. They are data points in a vast interconnected network that carries information about every relative who shares our bloodline. Understanding this reality helps us make more informed decisions about how and where we share our genetic and genealogical information.

It also underscores the remarkable power genealogy holds. What Mary Wilhelm Hinchman and the countless researchers before her built through decades of patient documentary research — a rich, interconnected record of family relationships stretching across generations — is exactly the kind of foundation that makes forensic genealogy possible. Family trees built with care and accuracy are not just personal treasures. They are contributions to the collective human record.

The Future of Forensic Genealogy

The field continues to evolve rapidly. Advances in DNA extraction technology allow investigators to obtain usable profiles from increasingly degraded samples. Machine learning tools are accelerating the tree-building process. Legal frameworks governing the use of genetic genealogy in criminal investigations are being developed and debated in legislatures across the country.

What began as a niche application of genealogical methods has become a recognized forensic discipline, taught in university programs and employed by law enforcement agencies nationwide. Forensic genealogists now work as professional consultants, expert witnesses, and advocates for the unidentified and the wrongly convicted.

For the Hinchman Heritage Society and our community of researchers, the rise of forensic genealogy is a reminder of why this work matters. The connections we trace, the records we preserve, and the stories we recover are part of something larger than any individual family. They are threads in the human story — and sometimes, tracing those threads can change the course of justice itself.