For the dozen years between 1974 and 1986, he rained down terror across the state of California. He went by many names: the East Side Rapist, the Visalia Ransacker, the Original Night Stalker, the Golden State Killer. And on Wednesday, law enforcement officials announced they think they finally have his real name: Joseph James DeAngelo. Police arrested the 72-year-old Tuesday; he’s accused of committing more than 50 rapes and 12 murders.

In the end, it wasn’t stakeouts or fingerprints or cell phone records that got him. It was a genealogy website.

FBI

Lead investigator Paul Holes, a retired Contra Costa County District Attorney inspector, told the Mercury News late Thursday night that his team used GEDmatch, a no-frills Florida-based website that pools raw genetic profiles shared publicly by their owners, to find the man believed to be one of California’s most notorious criminals. A spokeswoman for the Sacramento County District Attorney’s Office reached Friday morning would not comment or confirm the report.

GEDmatch—a reference to the data file format GEDCOM, developed by the Mormon church to share genealogical information—caters to curious folks searching for missing relatives or filling in family trees. The mostly volunteer-run platform exists “to provide DNA and genealogy tools for comparison and research services,” the site’s policy page states. Most of its tools for tracking down matches are free; users just have to register and upload copies of their raw DNA files exported from genetic testing services like 23andMe and Ancestry. These two companies don’t allow law enforcement to access their customer databases unless they get a court order. Neither 23andMe nor Ancestry was approached by investigators in this case, according to spokespeople for the companies.

But no court order would be needed to mine GEDmatch’s open-source database of more than 650,000 genetically connected profiles. Using sequence data somehow wrung from old crime scene samples, police could create a genetic profile for their suspect and and upload it to the free site. As the Sacramento Bee first reported, that gave them a pool of relatives who all shared some of that incriminating genetic material. Then they could use other clues—like age and sex and place of residence—to rule out suspects. Eventually the search narrowed down to just DeAngelo. To confirm their suspicions, police staked out his Citrus Heights home and obtained his DNA from something he discarded, then ran it against multiple crime scene samples. They were a match.

“It’s fitting that today is National DNA Day,” said Anne Marie Schubert, the Sacramento district attorney, at a press conference announcing the arrest Wednesday afternoon. A champion of genetic forensics, Schubert convened a task force two years ago to re-energize the cold case with DNA technology. “We found the needle in the haystack, and it was right here in Sacramento.”

After four decades of failure, no one could blame law enforcement officials for celebrating. But the methods they used to track down DeAngelo raise some serious questions about what constitutes due process and civil liberty in a time when commercial DNA testing is becoming more popular than ever.

FBI

DNA evidence has been a cornerstone of forensic science for decades, and rightly so. It’s way more accurate than hair or bite-mark analysis. But the routine DNA tests used by crime labs aren’t anything like what you get if you send your spit to a commercial testing company. Cops look at a panel of 20 regions of repeating locations in the genome that don’t code for proteins. Because those repeating sections vary so much from individual to individual, they’re good for matching two samples—but only if the suspect is already in the criminal databases maintained by US law enforcement. Investigators in the Golden State Killer case had long had DNA, but there was no one in their files with which to match it. And so the case went cold.


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