Advances in biotechnology such as the polymerase chain reaction and DNA sequencing are making it possible for scientists and doctors to make huge strides in treating diseases. However, they have also had an amazing impact on the ability of the police to both identify criminals – and to prove that people are innocent of crimes. The first ever murder conviction which was brought about as a result of DNA evidence also cleared a man of rape and murder using the same techniques. It is an astonishing story …

In 1983, fifteen year old Lynda Mann was raped and murdered in Narborough in Leicestershire. A semen sample was taken from her body, but at that point scientists could only tell the blood group and certain enzyme types from the evidence. Three years later another 15 year old girl, Dawn Ashworth, was also found raped and murdered in the same area. All the evidence pointed to it being the work of the same man. The semen samples showed that the blood groups matched.

The police had a suspect – a local man – who eventually confessed to Dawn’s murder but denied having anything to do with Lynda’s death. But Chief Constable Michael Hirst and Chief Superintendent David Baker were convinced that if he had committed one crime, he had committed both. They contacted Dr Alec Jeffreys and his team at Leicester University, who had published work showing how new DNA analysis techniques (what we now call DNA fingerprinting) could be used to help solve crimes.

When Alec Jeffreys ran a comparison between the semen from both rapes, and the blood of the suspect, he found that the crimes had certainly been carried out by the same man – but it wasn’t the man who had confessed!

David Baker then decided to set up a mass screening of all the adult males in the three villages in the area where the girls had lived and died. 5000 men gave samples, and DNA profiling was carried out on the 10% of the sample who had the same blood group as the murderer. The process in those early days was slow and drawn-out, and people in the Forensic Science Service worked long hours, putting in evenings and weekends, to deal with all the DNA and track down the killer. But no match with the DNA from the killer was found – what else could be done?

Even with the DNA evidence, the killer might have got away with it and lived to kill another day if it hadn’t been for an overheard conversation. A local woman heard a colleague boasting to someone that he had given his DNA sample in a false name – he had done a mate a favour and claimed to be Colin Pitchfork when he gave his saliva sample. The woman went to the police, the real Colin Pitchfork was arrested and DNA samples were taken. Sure enough, when the results came back, Pitchfork’s DNA profile matched that of the semen taken from the murdered girls. In 1988 Colin Pitchfork was jailed for life for taking the lives of the two young girls.