Retired police officer Joseph James DeAngelo has been arrested, accused of being the Golden State Killer. The case against him looks strong, so let me pause to celebrate the fall of a monster.
And then move on to wonder about how he was caught.
What the police did was to run DNA samples from old crime scenes – The Golden State Killer's last crime was in 1986 – and then compare them to profiles posted on genealogy web sites. They identified people who were probably related to their suspect. Then they used family trees posted online to find someone of that family who was the right age and lived in the right town. They identified DeAngelo as a possible suspect. Then they grabbed some of his trash to get a sample of his DNA "left in the public domain" and indeed he was a match to their crime scene samples.
Brilliant police work but I find it a bit creepy. Civil libertarians have always resisted letting the police build up a DNA library of the whole population, but that is pretty much what the DNA testing web sites are doing. This is new, rapidly advancing technology, so if it is already good enough to help the police zero in on DeAngelo it will soon be good enough to identify the author of every spit wad, fingerprint and stray hair left anywhere in the country. This is happening without your consent, because some relative of yours has already posted your family tree at Ancestry.com, and most likely some near relation has posted his or her DNA profile. This has already been used by adopted children to break through legal seals on their birth records and track their birth families, with traumatic results.
Another danger is that DNA technology can work from tiny samples. You leave DNA everywhere you go, on everything you touch. Crime scene DNA testing has already identified as least one incorrect suspect that I know of, the worker who built a duct where a body was later found. Fortunately the police sorted that one out, but do you trust them to do that in every case? A clever killer will now do his deed wearing surgical scrubs or a hazmat suit but be sure to leave lots of DNA around from another likely suspect. If there's a gang killing, and blood at the crime scene matches someone known to be active in a rival gang, will the police bother to investigate further? I imagine a world in which careful people will burn all their hair and fingernail parings like those terrified of witches used to do.
Anyway, that's the world we live in. Between your own internet history and family DNA posted online, strangers can now learn a vast amount of intimate stuff about you. This will help catch future serial killers but it is also bound to have lots of unanticipated effects.