How Genetic Genealogy Is Rewriting Criminal Justice

A New Kind of Detective Work

In April 2018, California investigators announced the arrest of Joseph James DeAngelo — a 72-year-old former police officer who was accused of being the Golden State Killer, responsible for at least 13 murders and 50 sexual assaults across California in the 1970s and 1980s.

DeAngelo had evaded capture for over 40 years. No tip had identified him. No witness had come forward. Law enforcement had his DNA from dozens of crime scenes but no match in any criminal database.

What broke the case was a technique that had never been used in a high-profile investigation before: investigative genetic genealogy. And once its power was demonstrated, the criminal justice system was never going to be the same.

How It Works

Investigative genetic genealogy uses consumer DNA databases — the same ones people use to find distant cousins and trace their ancestry — to identify unknown suspects in criminal cases.

The process works in stages:

Step 1 — Crime scene DNA. Investigators have a DNA sample from the crime scene — blood, semen, hair — but no match in law enforcement databases like CODIS.

Step 2 — Upload to genealogy database. The DNA profile is uploaded to a public genealogy database, most commonly GEDmatch, which allows users to upload raw DNA data from any testing service and compare it against millions of other profiles.

Step 3 — Find distant relatives. The database search returns partial DNA matches — people who share significant chunks of DNA with the unknown suspect. These matches indicate biological relatives: second cousins, third cousins, sometimes closer.

Step 4 — Build a family tree. Forensic genealogists work backward from the matches, constructing family trees for each relative using publicly available records — birth certificates, census data, obituaries, newspaper archives. They trace branches forward in time, looking for individuals in the right age range and geographic location who could be the suspect.

Step 5 — Narrow down suspects. Traditional investigation — surveillance, discarded DNA collection, background checks — is used to confirm or eliminate candidates until one remains.

In the Golden State Killer case, the process took investigators from an unknown DNA profile to a named suspect in just over three months.

The Case Backlog

Since DeAngelo's arrest, investigative genetic genealogy has been used to solve hundreds of cases across the United States — many of them cold cases that had been open for decades.

The technique has been particularly effective in cases involving unidentified remains. The Doe Network and similar organizations have worked with genealogists to give names back to John and Jane Does whose identities were never established through traditional means.

The technology's reach is expanding rapidly. As genealogy databases grow — GEDmatch alone has over 1.5 million profiles — the probability of finding a useful DNA match increases for any unknown sample. Researchers estimate that for individuals of European ancestry, a DNA sample can now be matched to a third cousin or closer relative in the majority of cases. For other ethnic groups, the databases remain less comprehensive, introducing a disparity in investigative reach.

The Privacy Question

The power of investigative genetic genealogy raises profound questions about genetic privacy — questions that go far beyond the individuals actually suspected of crimes.

When you submit your DNA to a genealogy service, you are not only revealing information about yourself. You are revealing information about every biological relative you have — including relatives who never consented to having their genetic information entered into any database.

If a third cousin of yours is an unknown suspect in a violent crime, law enforcement may use your DNA submission to identify them — without ever contacting you, without your knowledge, and without a warrant.

GEDmatch initially allowed law enforcement access to its database by default, then changed to an opt-in model in 2019 following significant public backlash. But the opt-in rate remains high enough that the tool remains effective.

The larger commercial databases — 23andMe and AncestryDNA — have maintained stronger privacy protections, refusing to provide law enforcement access without a valid legal process and disclosing the number of such requests in annual transparency reports. But legal processes can compel disclosure, and the definitions of what constitutes sufficient legal process vary by jurisdiction.

The Regulation Gap

In the United States, investigative genetic genealogy operates in a largely unregulated space.

In 2019, the Department of Justice issued interim guidelines governing federal use of the technique, requiring that it be used only in violent crime and unidentified remains cases, that other investigative methods be exhausted first, and that the results be used only to generate investigative leads rather than as standalone evidence. States have been slower to regulate.

Critics argue the guidelines are insufficient. They note that the technique can be used without a warrant, that the communities most impacted by law enforcement surveillance have the least power to resist it, and that genetic data — once collected — is extraordinarily difficult to delete or contain.

Proponents counter that investigative genetic genealogy is no different in principle from other forms of investigative lead generation, that the privacy intrusion is limited, and that the justice it has delivered to victims' families outweighs the theoretical risks.

Both sides make valid points. The conversation the public needs to have about genetic privacy — and specifically about the trade-offs between investigative power and civil liberties — is still only beginning.

Looking Forward

The technology will only become more powerful. Improvements in low-template DNA analysis allow investigators to work with samples too small or degraded for traditional testing. Forensic phenotyping can generate a predicted physical appearance from DNA alone. The databases will continue to grow.

The question is not whether investigative genetic genealogy will continue to be used. It will. The question is what guardrails society will put in place — and who will be at the table when those decisions are made.

For crime victims and their families, this technology represents hope that has been a long time coming. For civil libertarians and privacy advocates, it represents a surveillance capability with no clear limits. Both things can be true simultaneously.

NaturalQueen77 TV is committed to following developments in forensic technology and reporting on both the justice it delivers and the questions it raises.