So the Golden State Killer was found through DNA relatives on an ancestry site.
First thought: The cops can compel an ancestry site to look through their stuff for a match to a criminal?
Maybe, maybe not, but that didn't happen. They submitted his DNA to a site and looked for what relatives matched and used the matching relatives to get an idea who it could be. The ancestry site didn’t even know it happened.
Second thought: wait a minute, so they somehow submitted 40+ year old DNA to 23andme or Ancestry? How did that even work, they require a vial of spittle. Did they have a 40+ year old vial of spittle sitting around?
Answer: that didnt happen either. There is an ancestry matching site called GEDMatch that doesn't do its own DNA analysis. You can download your DNA info from another site like 23andme or ancestry and upload it to GEDMatch and do matching there. So the cops just took the DNA info they had, put it in the format needed for GEDmatch, and uploaded it.
I'm really glad they found the guy but GEDMatch is rightfujllyh outraged at how their services were abused. They don't want any random person to be able to upload DNA and use it to track down the person whose DNA it is. In this case, it was used by the cops to do something awesome, but there's no reason it couldn't have been used by any rando who for some reason was able to get a DNA profile from somebody. The assumption behind their service is that nobody would have a copy of a set of DNA data except the person whose data it was, who had a right to upload it and have it analyzed. That assumption turns out to be false.