The trouble with contamination

A case in Germany illustrates how easy it can be for contamination to sneak into labs from unexpected sources:

Police in Germany have admitted that a woman they have been hunting for more than 15 years never in fact existed.
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She was alternatively called the "woman without a face" and the "phantom of Heilbronn" after the city in southern Germany where she allegedly killed a policewoman.
Police suspicions were based on traces of identical female DNA they found at 40 crime scenes across southern Germany and Austria.
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Now it has been determined that the cotton swabs used to collect DNA had been contaminated accidently by a woman working at an unidentified factory in Bavaria.

The company selling the swabs did not claim they were DNA-free or certified for use in DNA analysis.