Tanya Van Cuylenborg, 18, and Jay Cook, 21, who were found murdered in 1987 in Washington StateSnohomish County Sheriff’s Office

Just three weeks ago, law enforcement in California announced the arrest of the Golden State Killer using DNA. The press conference was vague, but the details of the novel method soon trickled out: Joseph James DeAngelo was found by matching DNA from a crime scene with that of his distant relative on the genealogy site GEDmatch.

On Friday, police in Washington State announced the arrest of William Earl Talbott II for a double murder in 1987, and this time, they proudly announced the use of the same method of tracing distant relatives through DNA—a field known as genetic genealogy. Steven Armentrout, the president of Parabon NanoLabs, the forensics company that did the DNA analysis, spoke at the press conference. So did CeCe Moore, a genetic genealogist who now works with the company.

Parabon has jumped headlong into this technology. On May 8, it announced the creation of a new genetic-genealogy unit led by Moore. The company recently told BuzzFeed it had uploaded DNA from about 100 crime scenes to GEDmatch.com, with about 20 of them generating matches of a third cousin or closer. “I think there is going to be press around this very soon,” the company’s director of bioinformatics had said to BuzzFeed.

Moore and other genetic genealogists have been using a similar technique to find the families of adoptees for years. The raw data from 23andMe, AncestryDNA, and other DNA-testing services can be uploaded on a volunteer-run site called GEDmatch, which allows genealogists to compare segments of DNA. These tests are more sophisticated than the DNA tests police typically run, and they generate more data than is stored in the FBI’s CODIS database. These DNA segments can then be crossmatched with family trees and public records to find an adoptee’s birth family—or a criminal.

In the double murder in Washington State, the suspect’s DNA matched two relatives, both fairly close by the standards of this research: a second cousin and a half–first cousin once removed. The former relative was on the mother’s side, the latter the father’s side, so the suspect was not hard to identify. “No cases are easy, but when they are straightforward, it really falls into place very quickly,” says Moore.

She says she had been talking to Parabon for about a year and a half. She had initially hesitated to work on criminal cases because she was unsure of legal and ethical issues, especially if people uploading their DNA to GEDmatch were unaware police were trawling through the database. But the positive feedback since the Golden State Killer case convinced her to make the plunge. Plus the publicity of that case has made it well-known that police can search genealogy databases. Moore is not the only genetic genealogist doing this kind of work for police departments.

Now, the floodgates are open. The strangest part of this story may be that a small, volunteer-run website, GEDmatch.com, has become, as the genealogist Debbie Kennet has similarly observed, the de facto DNA and genealogy database for all of law enforcement.