From 2007 to 2009, German authorities searched for a female serial killer whose DNA had been found at six separate murder scenes. Just one problem: she didn’t exist.
In 2007 a police officer named Michèle Kiesewetter was shot in the head in Heilbronn, Germany. The investigators quickly found some DNA evidence and determined that it came from an Eastern European woman. Going into the crime databases, they found something alarming: the same DNA was found at the site of six other murders. There was a serial killer on the loose.
Aside from the DNA there was nothing else tying the murders together: no witnesses, hair, footprints, motives… so the suspect in these cases became known as the Phantom of Heilbronn. As the investigation continued her DNA was found at many other crime scenes: burglaries, robberies, and home invasions, going back as far as fourteen years before the murder. 300,000 Euros were offered for her capture. The Phantom was the biggest criminal mastermind since Professor Moriarty.
And, as it turns out, she was just as fictional. Well, the DNA came from a real woman, but she was not a criminal mastermind or a serial killer. She worked at a packaging factory. A packaging factory which processed, amongst other things… cotton swabs. In the process of packaging the swabs she had inadvertently contaminated them with her DNA. The swabs were used by police departments to collect DNA from crime scenes, and thus the test results kept pointing to this poor woman.
The mistake was identified when test results came in that made no sense and would have been impossible. As far as I can find out they never actually found the innocent woman, just worked out the origin of the DNA contamination and left it at that. They did eventually find the culprits in the police officer’s murder (neo-Nazi terrorists) and now cotton swabs are treated much more carefully when gathering evidence.
[Thanks to Gareth E. for suggesting this topic.]