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In 1993, a 62-year-old woman was found dead in her house in the German town of Idar-Oberstein. She had been strangled with a wire that was found near her body and although police initially had no suspects, the investigation found traces of DNA on the murder weapon.

The evidence was too little for the times and soon the case went cold. It wasn’t until eight years later that another murder investigation found traces of the very same DNA at the scene. Police were intrigued and rightfully began looking at the possibility of a single individual as the suspect in both crimes.

DNA analysis showed that the suspect was a woman, but this was not enough to point investigators in any specific direction.

Nobody expected what was about to happen next. In the following years, the woman’s DNA showed up at 40 different crime scenes in Germany, France, and Austria, prompting the police to admit the possibility of a female serial killer on the loose.

Authorities had nothing to go on except for the DNA, and the suspect became known as the Phantom Of Heilbron.

Crimes attributed to the Phantom Of Heilbron ranged from murders to burglaries and had investigators baffled, until in 2009 nine, a breakthrough occurred that made police question whether there had ever been a serial killer, or even a suspect at all.

Modern forensics allowed police to analyse the mitochondrial DNA from samples collected in Austria, and the results showed characteristics most often found among people in Eastern Europe and neighbouring Russia. A special task force named Parkplatz followed up on this tenuous lead until a startling revelation completely destroyed the Phantom of Heilbron theory.

In 2009, police finally learned that all the DNA evidence had been collected using cotton swabs from one specific source, and the DNA from the 16 years of crime was linked to a single woman who worked in the processing line of the factory that supplied the forensic swabs.

The cotton swabs used by many state police departments were found to have been contaminated before shipping. There never was a serial killer, to begin with.

As a result of this severe case of contamination, the International Organization for Standardization (ISO) had to publish new guidelines for the materials used to collect evidence, and these rules still govern the production and distribution of forensic material today

German police were finally able to put to bed the Phantom of Heilbron as the most prolific serial killer that never existed.

[source:wikipedia&ifls]