Earlier this month, detectives in California tracked down and arrested a suspect in a case that had gone unsolved for over 30 years: the rape and murder of 45 women by a criminal dubbed "The Golden State Killer."

How did they do it? With a tool that was most certainly not at their fingertips in the 1980s: Online genealogy websites.

Investigators were able to find their suspect, Joseph James Deangelo, by searching the free, open-source website GEDmatch for DNA that matched decades-old samples from one of the crime scenes. (The sample on the genealogy site did not come from Deangelo himself, but from one of his distant relatives.)

Medical ethicist Arthur Caplan said the case is a reminder that many people who use DNA testing services and genealogy websites are not aware of where their information goes or who has access to it.

"What companies are doing is they're hooking you into a fun, recreational thing ... and then they put all the DNA information from different people in a big database and they keep it," Caplan said.

Caplan believes that law enforcement officials should need to obtain a search warrant before accessing large databases of DNA information.

"I'm not against finding killers with DNA analysis. That's great. Go tell a judge and have someone sit there and make sure that what they're looking at doesn't violate any individual's rights," he said. "We don't have a [legal] procedure. That's what's missing here."