This 2007 murder was believed to be the work of the phantom killer
Police in Germany have admitted that a woman they have been hunting for more than 15 years never in fact existed.
Dubbed the "phantom of Heilbronn", the woman was described by police as the country's most dangerous woman.
Investigators had connected her to six murders and an unsolved death based on DNA traces found at the scene.
Police now acknowledge swabs used to collect DNA samples were contaminated by an innocent woman working in a factory in Bavaria.
Police suspected the unnamed woman of being a serial killer who over 16 years carried out a string of six murders, including strangling a pensioner.
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.
After finding her DNA at the scene of the murder of a 22-year policewoman from Heilbronn in 2007, police offered a 300,000 euro reward for information leading to her arrest.
However, police did not come any closer to identifying their most-sought suspect.
According to prosecutors in the south-western town of Saarbruecken, doubts about the existence of the "phantom killer" were raised when her DNA appeared on documents belonging to a person who had died in a fire.
When police first tried to identify the victim, they found the phantom's DNA on the dead person's ID. But in a subsequent test, no trace of the phantom's DNA could be found on the document.
That was the point at which alarm bells started ringing and investigators began to suspect that the test material itself may have been contaminated with DNA, prosecutors say.
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 puzzle of the phantom killer has been solved," said Volker Link, a prosecutor in Heilbronn.
One company making swabs said they were not intended for analytical, but only medical use, while another said that there had been no requirement for the swabs to be free of DNA.