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Tuesday, March 24, 2009

Thousands of 'cold cases' could be reopened thanks to new DNA technique

by Kate Devlin, Medical Correspondent

Scientists will now be able to use the technique in all serious crimes, after it proved successful in a series of pilots.

Police forces and forensic scientists are also combing the archives of thousands of so-called "cold cases", in which no-one has been convicted of the crime, for DNA samples which could be reassessed.

Called "DNA Boost", the new technique, developed by the FSS, allows scientists to create profiles from "mixed" samples, which contain genetic information from two or more people found on the same surface.

Previously scientists found it impossible to analyse many of these samples, which make up around 10 per cent of all those collected from scenes of crime.

"In the past it has been very difficult to unscramble these samples," said Mark Pearse, from the FSS, "which means they cannot then be searched for in the DNA database."

Now, however, the FSS has developed computer software capable of matching "pairs" of this scrambled data together, creating possible DNA matches.

These can then be fed into the database, which currently contains the details of about four million people, identifying potential suspects.

These can then be suggested to the police as possible leads for their investigations.

Martin Bill, from the FSS, said that DNA Boost was the greatest breakthrough in forensic science since the introduction of low copy number testing, which allowed profiles to be built from tiny samples of DNA, in the late 1990s.

"There will be thousands of cases in our archives that could benefit from this technique," he added.

The technique was "scientifically robust" he insisted.

He added: "We feel that this approach is scientifically very sound and that there is little potential for both false inclusion and false exclusion."

However, he added that DNA Boost would not replace the judgement and interpretation of scientists and police on how genetic information came to be fopund at a crime scene.

Although it is rare that blood or semen samples to become mixed, officers often find that samples of cells taken from surfaces such as tabletops or cigarettes can contain the DNA of more than on person.

A DNA profile is a "genetic fingerprint", unique to each person.

They can be identified from analysis of cells, including from tiny samples of blood, semen, saliva, skin or even sweat.

Professor John Brookfield, an expert in forensic science from Nottingham University, said that researchers had struggled for years to deal with the problem of mixed samples.

"Often the problem is that you do not get an even proportion of the two components, making them a real challenge to analyse for a profile," he said.

The software is available for use in all cases referred to the FSS, after trials carried out in four police forces, West Yorkshire, South Yorkshire, Humberside and Northumbria, proved successful.


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