Genealogy databases helped law enforcement catch a serial killer that had been operating in California between 1976 and 1984. The alleged murderer has been identified as a former police officer, who had left his DNA at the scene of a rape and murder.
The investigators uploaded that sample of the killer's DNA to Ancestry and 23andme. They also used GEDmatch, which compiles data from the most commonly used DNA companies and usually just helps people to find family members. Learn more about how they identified the suspect from the video.
Naturally, the use of this information has spurned concerns about privacy. The police did not tell GEDmatch what their intentions were before doing their search. The bottom line is that if you want your genetic information to remain completely under your control, don't send it to any testing companies. This investigative technique has been used before, and likely will be again.