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.