How Did Police Really Find the Golden State Killer Suspect?

alleged Golden State Killer

Slate reports:

Perhaps the biggest mystery now is just how law enforcement identified DeAngelo [the alleged Golden State Killer] as a person of interest in the crimes 40 years after they began. So far, officials have declined to explain, but [Paul Haynes who researched the killings] has his suspicions. During the press conference, Sheriff Scott Jones said, “Although it was DNA ultimately that led us down the road, there was a lot of places that road could have led.” Haynes thinks it likely that investigators used DNA markers posted on genealogy websites to identify a possible ancestor of the killer and then followed the ancestor’s family tree down to the present, looking for male descendants who fit the profile. But this, he cautions, is only an educated guess, and what evidence law enforcement used to pinpoint DeAngelo is “the No. 1 thing I want to know.”

In this case, law enforcement might have used this technique to identify a very bad guy. But how long before government uses the technique to go after someone for some reason that doesn't violate NAP?

-Robert Wenzel