They used "crime scene" samples and what they are calling “abandoned” DNA from the suspect ("You leave your DNA in a place that is a public domain” they don't need a warrant?)
https://www.nytimes.com/2018/04/26/us/golden-state-killer.ht...
Im guessing that any relative has a right to divulge his dna and rat out a blood relative in a situation like this, but I doubt people actually consent to that use when they are looking at a genealogy site.