@Alex D
> Is it such a bad idea for the police to have a database of DNA?
Ask Raymond Easton, the guy who, although suffering from Parkinsons Disease (which meant that he could barely walk to the front door unaided) was, none the less, arrested by Swindon Police on behalf of Greater Manchester Police because his DNA was "found" at the scene of a burglary. Except it turned out that it wasn't his DNA and it was a false positive.
http://archive.thisiswiltshire.co.uk/2000/8/15/238098.html
The fact that the guy was virtually immobile appeared to be utterly irrelevant to the Police, who in their simple minded way, decided that because there was a DNA match, he *must* have been the criminal.
Now imagine that you sneeze into a hanky, someone else steals that hanky and drops it a the scene of a crime. "Oho!" says Mr Plod, "Let's check our database... Aha! Mr Alex D I arrest you for the crime of not thinking a bit more about the risks of false positives..."