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Ideas | S.I. Rosenbaum

Genetic data can track down criminals — and everyone else

Joseph James DeAngelo, the suspected Golden State Killer, appears in court for his arraignment on April 27 in Sacramento, Calif. Justin Sullivan/Getty Images

It was nearing 2 a.m. when they found her. Margaret Press could only gasp. “I have chills down my back,” she told her partner, Colleen Fitzpatrick.

By matching the DNA profile off a long-dead woman known only as Buckskin Girl against a public genetic data archive, the two had identified her as a woman who had gone missing 37 years before.

It was the first time the technique had been used. Only a few weeks later, police in California announced they’d independently used the same process to track down a man accused of being the serial rapist and murderer known as the Golden State Killer.

Neither the suspected Golden State Killer nor Buckskin Girl had a genetic profile in the archive used to identify them. But it didn’t matter — in both cases, someone in their family tree was in the archive, and that was enough to lead investigators to their target.


Today, an estimated 12 million to 15 million Americans have have sequenced their DNA using one of a few commercial companies such as Ancestry.com or 23AndMe. About a million of them have gone on to enter the resulting DNA profile at GEDmatch, a public, self-service archive based in Florida — kind of a Wikipedia for genetic data. At this point, almost everyone has at least one distant relative — a fourth or fifth cousin, perhaps — whose DNA profile is publicly available. And if they don’t, they will soon.

This means that we could be entering an era in which it becomes possible to find every rapist, every killer who leaves behind a genetic trace. The technology could usher in the era of mass exonerations. Or it could herald something more sinister — a surveillance state in which your distant relatives’ DNA can testify against you.

“We want the bad guys caught and prosecuted, but there’s a limit,” said legal scholar Mark Rothstein. “The new power of this technology is going to force us to think about how far we think that ought to extend.”


But the fact remains that for most Americans, the choice of whether or not to share genetic information is becoming moot — if it’s not already.

Forensic genealogy has been around for decades — Fitzpatrick helped pioneer the field and literally wrote the book on it — but in the past, the idea of using a public archive to identify forensic DNA samples from a suspect or an unidentified corpse (a “John Doe” or “Jane Doe”) was considered a fool’s errand.

The larger commercial databases don’t allow forensic use of their data. GEDmatch’s policies are more lenient, but its archive was considered too small to yield results. (The founders of the site declined to comment on this story.)

Plus there was the problem of preparing a good DNA sample for a system designed for the living. Nobody thought John and Jane Doe could spit into a vial because they’re dead.

But last year, Press and Fitzpatrick heard about a hobbyist who’d managed to build a genetic profile of his dead father using a years-old tissue sample. They decided it was worth a try, and founded a nonprofit called DNA Doe.

Working together with law enforcement, they sequenced Buckskin Girl’s DNA and prepared it so that it could be uploaded to GEDmatch.

It took only a day for the results to process and they found a match: a many-times-removed cousin. That narrowed their search to people descended from their common ancestor.


As it grew late, they combed through family trees online. They found one made by an amateur genealogist from Arkansas who had marked his own daughter, Marcia King, “missing — presumed dead” in the same year Buckskin Girl had been discovered.

They knew they’d found her. “It’s the most exciting rush you can imagine,” Press said.

The detectives in the Golden State Killer case haven’t been as forthcoming about their process. But it’s likely they followed the same procedure: finding a cousin through GEDmatch, and then looking for descendant of the common ancestor who matched the killer’s profile.

“So in essence, the police were conducting a fishing expedition on 900,000 people who had no idea that their data was going to be used for this,” said Leah Larkin, a genetic genealogist who followed the cases closely.

The people who upload their information to GEDmatch — “geeky” genealogy enthusiasts — knew the data they shared was public, but they probably didn’t expect to become part of a forensic investigation, Larkin said.

In the genealogy world, reaction to the news of the two cases has been mostly positive. “I’m surprised — I thought people would be more alarmed. But it’s really hard to be sympathetic toward a serial killer,” she said. “This is such an incredibly positive and powerful use of this technology, it’s hard to argue with how awesome it is.”

Not everyone feels that way. “What kind of country do we want?” said Mark Rothstein, founding director of the Institute for Bioethics, Health Policy and Law at the University of Louisville School of Medicine. “You could have a requirement that every newborn be screened [and their genetic information archived] . . . and we can get there by little incremental steps that seem to be justified by terrible crimes and our eagerness to solve them. But it’s not a very pretty picture of a country that values liberty and freedom.”


Police already have compiled a genetic archive of their own: the Combined DNA Index System or CODIS, established in the 1990s, which contains both DNA collected from crime scenes and the DNA profiles of convicted criminals.

By design, in the interests of privacy, the profiles in CODIS aren’t nearly as detailed as the ones in GEDmatch — you couldn’t use it to find a fifth cousin. But Rothstein wonders if the Golden State Killer and Buckskin Girl cases might lead to more aggressive and comprehensive genetic surveillance, not just for felons but for everyone.

“We need to rein in these practices,” he said. “I dont think its too late to put limits on law enforcement that are reasonable.”

Larkin, the genealogist, also believes that expanded law-enforcement uses of genetic data are in the future. And she says that the prevalence of commercial DNA profiling has prepared us to accept it.

“When the CODIS database was set up, people were less comfortable with using DNA in the fist place,” she said. “But now that perhaps 15 million people have taken these DNA tests, given that we now live in a world where people do this just for fun, obviously they are comfortable. Perhaps the mood has shifted.”


After all, she said, if you were born in the United States, it’s nearly certain some part of your genetic data — carried by a cousin, close or distant — is already there, sitting in an archive, waiting to be read.

S.I. Rosenbaum can be reached at si@arrr.net. Follow her on Twitter @sirosenbaum.