UK Police Want DNA of 'Potential Offenders'
AFAIK, there have been two infamous false-positive cases in recent years. These are just the ones we hear about as they are the most egregious. Despite all the other contrary evidence, the DNA 'matches' led the inquiry and resulted in the investigation and arrest of individuals who could not possibly have been involved in the crimes. It is a major concern that the compelling evidence of innocence (like being 200 miles away at the time of the crime) will take a back-seat to the supposedly infallible "DNA match".
There are reports that 1 in 8 DNA records on the database are incorrectly filed.