German authorities have ended their search for a female serial killer after discovering that DNA thought to be from 40 crime scenes actually came from a woman who packed the cotton swabs used to gather evidence.

The German police collected DNA from the scenes of crimes ranging from break-ins to murder. The samples were stored on a DNA database and matches began to appear. One woman's DNA had been collected at all the scenes.

The mystery serial killer was assumed to be behind the strangling of a pensioner in 1993, the shooting of a policewoman in 2007 and four killings in between. Also on the non-existent killer's rap sheet were a restaurant break-in and burglaries.

Police were stumped by the lack of any pattern to the crimes except that they were all committed in south west Germany, France and Austria. They offered a €300,000 reward for information about the supposed killer.

German authorities grew suspicious, though, and someone had a flash of inspiration and conducted tests at suppliers' factories. They found that of 96 swabs that had not yet been used, seven contained the DNA of the supposed mystery killer.

In England, DNA evidence can be collected from anyone taken in for questioning by police. It can be kept even if that person is not convicted or even charged with a crime.

Around 4.5 million records are currently on the UK DNA database, and 850,000 of those are said to belong to people who have never been convicted of a crime. 

It's soon going to be too dangerous in England to blow your nose for fear of leaving traces of DNA.

The European Court of Human Rights (ECHR) ruled last year that the retention of innocent people's records is a breach of their human rights as protected by the European Convention on Human Rights.