Fun fact, they can sometimes narrow down crime scene DNA to just a single person by having enough partial matches from their (potentially distant) relatives. I can't remember which DNA database was used, but some cases were solved this way, IIRC it introduced a bunch of legal questions about if you can search a database in that way.

I think this was the article that talked about this (apologies for the paywall): https://www.nytimes.com/2021/12/27/magazine/dna-test-crime-i...