Thomas Fuller in the New York Times:
The Golden State Killer raped and murdered victims all across the state of California in an era before Google searches and social media, a time when the police relied on shoe leather, not cellphone records or big data.
But it was technology that got him. The suspect, Joseph James DeAngelo, 72, was arrested by the police on Tuesday. Investigators accuse him of committing more than 50 rapes and 12 murders.
Investigators apparently took DNA evidence from crime scenes and plugged it into a DNA-based genealogy website—23andMe or one if its competitors—and found the people who turned up as relatives, using their family trees to close in on the suspect, Joseph James DeAngelo.
Then they followed him around until he left an “abandoned” DNA sample—something containing his DNA—in a public place. The investigators took that DNA sample and ran it against their crime-scene samples, at which point they became convinced they have found a serial killer and rapist who terrorized California in the 70s and early 80s.
I’d never thought of this use of voluntary DNA databases before, but it’s kind of brilliant. A suspect doesn’t have to be in the database; their presence can be inferred by triangulating the relatives who are in the database. I imagine we’ll be seeing several court cases and changes to terms of service if this sort of detective work becomes more widespread.