When companies like Ancestry.com and 23andMe first invited people to send in their DNA for genealogy tracing and medical diagnostic tests, privacy advocates warned about the creation of giant genetic databases that might one day be used against participants by law enforcement. DNA, after all, can be a key to solving crimes. It “has serious information about you and your family,” genetic privacy advocate Jeremy Gruber told me back in 2010 when such services were just getting popular.

Now, five years later, when 23andMe and Ancestry both have over a million customers, those warnings are looking prescient. “Your relative’s DNA could turn you into a suspect,” warns Wired, writing about a case from earlier this year, in which New Orleans filmmaker Michael Usry became a suspect in an unsolved murder case after cops did a familial genetic search using semen collected in 1996. The cops searched an Ancestry.com database and got a familial match to a saliva sample Usry’s father had given years earlier. Usry was ultimately determined to be innocent and the Electronic Frontier Foundation called it a “wild goose chase” that demonstrated “the very real threats to privacy and civil liberties posed by law enforcement access to private genetic databases.”

The FBI maintains a national genetic database with samples from convicts and arrestees, but this was the most public example of cops turning to private genetic databases to find a suspect. But it’s not the only time it’s happened, and it means that people who submitted genetic samples for reasons of health, curiosity, or to advance science could now end up in a genetic line-up of criminal suspects.