Yesterday several police departments in California announced the arrest of the "Golden State Killer," who killed a dozen people between 1978 and 1986 and has been accused of over 50 rapes. At the time, investigators said DNA played a role in identifying former Auburn, CA police officer Joseph James DeAngelo, and today went a step further with the explanation.

The LA Times and New York Times report that investigators took DNA samples from the old crime scenes and plugged them into online databases, looking for familiar matches that would help narrow down the suspect. The Olympian reports that by combing through family trees of partial matches they focused on DeAngelo, who was the right age and had lived in some of the areas. Before arresting the subject they got a DNA sample from something DeAngelo had discarded and checked for a match. That match led to his arrest and charges for two of the murders, with more expected to follow.