Apparently the German police spent over a decade trying to find an untraceable serial killer - the DNA samples found at multiple murders (with very different MOs) showed it was a woman of East European heritage. But witnesses all gave contradictory descriptions of her appearance and the police couldn't track her down. Sounded very much like a female Keyser Soze.
Eventually in a lucky break they found a match for the DNA - it turned out to match that of a woman working at the factory that manufactured the cotton swabs that the German police used to take DNA samples (these particular swabs weren't supposed to be used for that purpose and were not certified "clean").
news.bbc.co.uk
(I nicked this story from the podcast of the QI TV program...not really P&N as it's a ten-year old story so not N, but still thought it was funny in a very grim kind of way)
Eventually in a lucky break they found a match for the DNA - it turned out to match that of a woman working at the factory that manufactured the cotton swabs that the German police used to take DNA samples (these particular swabs weren't supposed to be used for that purpose and were not certified "clean").
BBC NEWS | Europe | 'DNA bungle' haunts German police
news.bbc.co.uk
(I nicked this story from the podcast of the QI TV program...not really P&N as it's a ten-year old story so not N, but still thought it was funny in a very grim kind of way)