I was watching some police documentary show a long time ago - and it was either the FBI or the police that needed a murder suspect's DNA - they brought him in f

I was watching some police documentary show a long time ago - and it was either the FBI or the police that needed a murder suspect's DNA - they brought him in for questioning, and asked him for a sample, and he declined. They had pretty compelling circumstantial evidence, so what they did was follow him around for 2 or 3 weeks to all of the public places he went, looking to get a left-behind hair, a swab of spit, a used soda can, food, any sample of his DNA they could use to test it against the murder scene evidence. This guy knows this is going on, and is playing cat and mouse with them, covering all of this DNA tracks - being careful to not leave anything for them. He eventually absent-mindedly spits on the sidewalk and they dab it up with cotton swabs, run the tests, and get the match, and arrest him. My point is, if somebody wants your DNA, even if you spend your entire day methodically covering your tracks because you're a murderer and you know it will send you to jail for life, you will eventually leave a trace somewhere. It's just the nature of our biology - it isn't the case that your DNA is a secret, and your body is a vault, and submitting this test is giving away that secret. In the case of submitting it here, I cannot imagine that any government agency that has the need for your DNA for some particular reason would think this was the best way to get it. (Hope this didn't serve to just make you more paranoid...)