You’ve probably seen the headline in some form: “Cold case solved with a DNA website.” It sounds like somebody pressed a button. It’s a good story because it isn’t anything like that.
The method is called forensic genetic genealogy, and it first burst into public view in April 2018, when an arrest was announced in the Golden State Killer case. That case involved a string of murders and more than 50 rapes across California between 1974 and 1986, and the investigation had gone cold for decades. The DNA was in an evidence file the whole time. It just didn’t match anyone in any police database. What finally cracked it wasn’t a new lab trick. It was a family tree.
What Is Forensic Genetic Genealogy?
It’s a method that combines DNA recovered from a crime scene with public genealogy databases, then uses family-tree research to work out who the DNA belongs to. Instead of looking for a direct match to the suspect, investigators look for that person’s relatives, sometimes very distant ones, and build outward from there.
The Electronic Frontier Foundation describes the start of the process this way: a genealogist uploads the DNA data to a consumer genealogy site, and the site’s algorithm returns a list of biological relatives and estimates of how closely they’re related.
Stage One: The Evidence
It begins with a DNA profile from the crime scene, which might come from a sample that’s decades old. If that profile doesn’t match anyone in the usual law enforcement databases, the case stalls. That’s where genealogy picks up.
Stage Two: The Database
The profile goes into a genealogy database like GEDmatch, where users have voluntarily shared their own DNA. What comes back isn’t the suspect. It’s usually a list of distant relatives, like third or fourth cousins, who have no idea they’re connected to a case.
Stage Three: The Family Tree
This is the slow, detective-like part. Genealogists use public records to trace those relatives back to common ancestors, then forward through the generations until the tree points to a small number of people. It’s painstaking work, building out dozens or even hundreds of relatives by hand.
Stage Four: The Confirmation
A family tree is a lead, not proof. Police still need a legally obtained DNA sample from the person of interest to compare against the crime scene evidence. In the Golden State Killer case, investigators gathered discarded DNA from the suspect and compared it with crime-scene evidence to help confirm him.
Cases That Show What It Can Do
According to Stanford, the identification of Marcia King in 2018 came after just a few hours of searching, and two weeks later police announced the Golden State Killer arrest.
Another is the 1981 murder of Anna Marie Hlavka in Portland. Detectives sent the case to Parabon NanoLabs, and TechCrunch reported that the genealogist identified the killer as Jerry Walter McFadden, a man who had already been executed in Texas in 1999. Sometimes the answer arrives long after it can lead to a trial.
And in Pennsylvania, CNN covered how the method helped solve the 1992 killing of schoolteacher Christy Mirack in 2018.
So Is It Really “Overnight”?
No. A study published in ScienceDirect looked at publicly reported cases cleared through forensic genetic genealogy through 2020 and found that it took an average of 12.1 months to clear a case. The Stanford piece says the same: while King was identified in hours, most cases take over a year.
The searching can be quick. The genealogy is the slow part. Stanford reported that the method had cleared more than 400 cases in the U.S. at that point, and that’s a lot of families getting answers. But it isn’t a magic button.
The Catch: Privacy and Mistakes
Here’s the awkward truth about the technology. When you upload your DNA to a public database, you also expose information about relatives who never agreed to anything. After the Golden State Killer case, GEDmatch changed its confidentiality statement to say law enforcement could search its data, as one bioethics paper notes.
There’s also the risk of getting it wrong. A PBS NewsHour report explored how genetic genealogy can help solve cases but can also point at the wrong person, which is why investigators rely on the confirmation stage. And rules vary from place to place. A recent European legal analysis argues that police use of genetic genealogy would need to be clearly justified under privacy law.
The Bottom Line
Forensic genetic genealogy hasn’t made cold cases easy. What it has done is give investigators a new way in when the usual databases come up empty. It’s slow, it takes skilled genealogists, and it raises real privacy questions. But for families who waited decades for a name, it has delivered something that once felt impossible.
Want more unsolved cases and strange histories? Browse our Mysteries section.
