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Colin Pitchfork - first murder conviction on DNA evidence also clears the prime suspect

Two schoolgirls who were murdered in the small town of Narborough in Leicestershire in 1983 and 1986 sparked a murder hunt that was only to be resolved by a intelligence-led screen, eventually leading to the conviction of a local man - Colin Pitchfork.

In 1983, a 15-year-old schoolgirl was found raped and murdered. A semen sample taken from Lynda Mann’s body was found to belong to a person with type A blood group and an enzyme profile, which matched 10 per cent of the adult male population. At that time, with no other leads or forensic evidence, the murder hunt was eventually wound down.

Three years later, Dawn Ashworth, also 15, was found strangled and sexually assaulted in the same town. Police were convinced the same assailant had committed both murders. Semen samples recovered from Dawn’s body revealed her attacker had the same blood type as Lynda’s murderer.

The prime suspect was a local boy, who after questioning revealed previously unreleased details about Dawn Ashworth’s body. Further questioning led to his confession but he denied any involvement in the first murder – that of Lynda Mann.

Convinced that he had committed both crimes, officers from Leicestershire Constabulary contacted Professor Sir Alec Jeffreys at Leicester University who had developed a technique for creating DNA profiles. Dr Jeffreys - along with Dr Peter Gill and Dr Dave Werrett of the Forensic Science Service (FSS) - had jointly published the first paper on applying DNA profiling to forensic science. Significantly, in 1985, they were the first to demonstrate that DNA could be obtained from crime stains, which proved vital in this case.

Dr Gill said: "I was responsible for developing all of the DNA extraction techniques and demonstrating that it was possible after all to obtain DNA profiles from old stains. The biggest achievement was developing the preferential extraction method to separate sperm from vaginal cells – without this method it would have been difficult to use DNA in rape cases."

Using this technique Dr Jeffreys compared semen samples from both murders against a blood sample from the suspect, which conclusively proved that both girls were killed by the same man, but not the suspect. The police then contacted the FSS to verify Dr Jeffrey’s results and decide which direction to take the investigation.

Peter Gill said: "Since the technique had not been used in criminal casework before, the FSS were asked by the police to confirm Dr Jeffrey’s conclusions. Accordingly, we carried out further tests and indeed demonstrated that the prime suspect could be excluded."

This suspect became the first person in the world to be exonerated of murder through the use of DNA profiling. Professor Alec Jeffreys said " I have no doubt whatsoever that he would have been found guilty had it not been for DNA evidence. That was a remarkable occurrence."

The police then decided to undertake the world’s first DNA intelligence-led screen. All adult males in three villages – a total of 5,000 men - were asked to volunteer and provide blood or saliva samples. Blood grouping was performed and DNA profiling carried out by the FSS on the 10 per cent of men who had the same blood type as the killer.

The murderer almost escaped again by getting a friend to give blood in his name. However, this friend was later overheard talking about the switch and that he’d given his sample masquerading as Colin Pitchfork.

A local baker, Colin Pitchfork was arrested and his DNA profile matched with the semen from both murders. In 1988 he was sentenced to life for the two murders.

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