German investigators' search for a mysterious suspected killer has ended with an embarrassing discovery: identical DNA traces common to dozens of crime scenes stemmed from contaminated cotton swabs.

The DNA had been found at the scenes of about 40 crimes over recent years in Germany, Austria and France, ranging from restaurant break-ins to the shooting of a policewoman. The common DNA prompted police to search for a woman German media called the "phantom killer."

However, officials said Friday they had determined that the DNA came from an innocent woman at an unidentified Bavarian packaging company involved in producing the cotton swabs used to collect evidence.

"The puzzle of the phantom killer has been solved," said Volker Link, a prosecutor from Heilbronn — the scene of a policewoman's fatal 2007 shooting, the most prominent crime linked to the mystery suspect.

Doubts about the "phantom killer" theory surfaced this week, and officials took saliva samples from workers involved in making the swabs.

They examined 96 unused swabs, and found that seven carried small DNA traces matching those of the mystery suspect.

Greiner Bio-One GmbH, one of the companies that makes the swabs, said earlier Friday that they were intended for medical rather than analytical use. Another manufacturer, Boehm Plastics, said its customers had not specified that the swabs must be free of DNA.

Germany's Federal Criminal Police Office said it would look into ways of ensuring that the DNA contamination is not repeated in future.