Your DNA and fingerprints are literally everywhere you go, and they don't decay as soon as you leave. Hell, even passing close by a person can transfer your DNA to their clothes.
replyIf the cops have a DNA Database, they "just" need to collect all DNA from a crime scene to compile a list of suspects, and by doing so, they're flipping the question of guilt around, you're no longer innocent until proven guilty, but guilty until proven innocent. You now have to prove you didn't "do it".
All the biometrics technologies are not perfect, e.g. there is a small chance of false positive, be it fingerprints, DNA, hair analysis, etc.
replyVeritasium had a nice video about this biometrics errors:
How could random prints be falsely linked to me if my prints are not in a database? It can only happen if they are.
replyYou can be falsely linked to a crime without biometric evidence and excluded on the basis of biometric evidence
replyThat can also be trivially done without a biometrics database: just collect and compare when they become a suspect!
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