Phantom of Heilbronn

Phantom of Heilbronn, or "Woman Without a Face" is the name of a suspected female serial killer. The killer is only known from DNA evidence. This evidence was present at different crime scenes in Austria, France, and Germany. The crimes were committed (or happened) between 1993 and 2009. Six of the crimes were murders. One of the murders was that of Michèle Kieswetter, a police officer. She was killed in Heilbronn on 25 April 2007.
The DNA had been found in 40 different crime scenes. There were many types of crimes committed - from burglaries to killings. In late March 2009, investigators concluded that the "Phantom" criminal did not exist. The DNA recovered at the crime scenes had already been present on the cotton swabs used for collecting DNA samples. The DNA belonged to a woman who worked at the factory where they were made.
The events were fictionalized in different serial episodes. 
Investigation.
An analysis of the mitochondrial DNA from the samples collected in Austria showed that it was most often found among people in Eastern Europe and neighboring Russia. This was not discovered in the German investigations. The analysis of mitochondrial DNA done in criminal proceedings is limited. The analysis could only determine a few other personal attributes of a suspect apart from sex. The killer existence was disputed, but is now said to be untrue.
The investigations focused on a special task force "parking lot" at the Heilbronn police department. In January 2009, the reward for clues regarding the whereabouts of the person was increased to €300,000.
The existence of the "Phantom" had been doubted earlier, but in March 2009, the case took a new turn. Investigators discovered the DNA profile on the burned body of a male asylum-seeker in France. This was an anomaly, since the profile was of a female. They subsequently came to the conclusion that the mysterious criminal did not exist. They found that the laboratory results were the due to the cotton buds used for DNA collection being contaminated. Although sterile, the swabs are not certified for human DNA collection.
The cotton swabs used by many state police departments were found to have been contaminated before shipping. It was found that the contaminated swabs all came from the same factory, which employs several Eastern European women who fit the type the DNA was assumed to match. Bavaria, although a region central to the crimes, obtained their swabs from a different factory. They had no reports of crimes committed by the Phantom.
Associated crimes.
The DNA attributed to the "Phantom" was found at the scene, as well as purportedly at the sites of the following crimes:
Conclusion.
As a consequence of this severe case of contamination with human DNA in a series of forensic investigations, the International Organization for Standardization (ISO) published the standard ISO 18385 in 2016. ISO 18385 defines the requirements for producing consumables free of human DNA contamination for collecting biological evidence at crime scenes. The requirement reads: "Minimizing the risk of human DNA contamination in products used to collect, store and analyse biological material for forensic purposes".