The false positive rate increases the more samples you test against. The same is even more true of something as flaky as fingerprint comparison (bullet or human). The appropriate method is to gather DNA from a crime scene and only compare against DNA from people who are already suspects for other reasons.For the past 20 years I have been wondering why governments weren't taking DNA samples from babies on day one. Just because your DNA was found at a crime scene doesn't mean you are guilty. Same way you are not automatically guilty if your finger prints were found at a crime scene. The justice system still applies. It will at least give investigators a starting point to find suspects (or rule them out), instead of having unknown DNA samples on a shelf for a 25 year old cold case. But some MyBB forumite will probably tell me why my opinion is wrong.