[Spktyr]

In that case, they didn’t need a warrant. They used an open database created with voluntarily submitted samples and privacy waivers.

[TornadoAlley3]

Correct. They had crime scene DNA. They sent the unknown suspect's DNA to the genealogy company. They got back matching relatives data. They created a family tree and narrowed the list by male and age.

In BTK they had crime scene DNA and Dennis Rader name but not his DNA. They learned his daughter was a student at Kansas State. They checked with the on campus clinic and discovered she had a Pap smear on file there. Search warrant was granted for DNA testing of the Pap smear.