how can there be a wrong sample? if the sample leads to someone that they can prosecute, it can't be wrong. only guilty leave DNA samples at crime scenes. this is known.
Pretty sure this is sarcasm, but for general interest I'll mention the Phantom of Heilbronn (https://en.wikipedia.org/wiki/Phantom_of_Heilbronn), "responsible" for multiple murders, but really just an employee at the company that made the cotton swabs that got used for DNA collection.
Yes on the sarcasm, but even better on you for posting an interesting link for a reply.