German police spent 16 years hunting a serial killer, known as the "Phantom of Heilbronn," who left behind the same DNA at every crime scene throughout the country. The killer was thought to be behind a string of 40 crimes and proved impossible to identify despite the best efforts of police. The only definitive evidence recovered from crime scenes was DNA indicating the killer was a woman of Eastern European descent. However, when investigators discovered the source of the genetic material, they found an average worker at a cotton swab factory. The discovery of the real identity of the killer led to the discovery of an elusive serial killer. The Phantom's DNA was found to match that of documents belonging to a person who had died in a fire, but subsequent retesting of these same documents revealed no trace of it.