Mark Hughes: Why DNA profiling is not just about convicting the guilty

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The Independent Online

The acquittal of Sean Hodgson is the latest case to benefit from the enhancement of DNA profiling techniques.

After being developed in 1984 by the British scientist Sir Alec Jeffreys, DNA profiling was used for the first time four years later in a criminal case in Leicester, when Colin Pitchfork was convicted of killing two schoolgirls.

The case was also the first to use DNA testing to exonerate a suspect: a local boy confessed to one of the murders but a blood sample proved he was not responsible.

In 1995, the national DNA database was set up with a view to helping the police secure convictions. It currently holds the DNA of more than four million people. Controversy surrounds the system whereby anyone arrested with an offence in Britain – no matter whether or not they are eventually charged or convicted – has their DNA taken. Those in opposition claim it criminalises the innocent, while supporters point to a long list of DNA-related convictions and acquittals.

Last year, one of Britain's most high-profile murder cases was solved when Robert Napper admitted killing Rachel Nickell on Wimbledon Common in 1992. Napper's confession came after forensic advances allowed scientists to examine tiny DNA samples and find a match that had only a one-in-1.4 million chance of being wrong. The significance of the DNA cannot be underestimated in this case, as Napper had told detectives that he would only confess to the killing if forensic evidence linked him.

The technique is so sophisticated that it does not always need the actual suspect's DNA to further investigations. In 2003, Jeffrey Gafoor was jailed for the murder of Cardiff prostitute Lynette White. The investigation had stagnated since 1992 after three men's wrong convictions were quashed of the murder. But then a young relative of Gafoor was arrested for an unrelated offence and placed on the DNA database. His profile led officers to Gafoor. DNA evidence can also allow the innocent to walk free, as yesterday's decision shows.