One of the most important uses of DNA testing is in criminal investigation, where it provides evidence that helps to prove that some crime suspects are guilty or others are innocent. The very first use of DNA testing in a criminal case was in 1985 in Great Britain, when a man confessed to killing a young woman in the English countryside. Because police had found samples of the killer's DNA at the scene of the crime, a biologist suggested that it might be possible to compare that DNA to some from the confessor's blood. To everyone's surprise, the tests showed that he
was not the killer. Nor was he guilty of a similar murder that had happened some time earlier. At
that point he admitted that he had confessed to the crimes out of fear and police pressure. The
police then asked 5,000 local men for samples of their blood, and DNA testing revealed that one
of them was the real murderer, so the first man was set free.