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Last Updated: Thursday, 20 December 2007, 17:00 GMT
Verdict raises DNA evidence doubt
By Michael Buchanan
BBC News

Omagh bomb
29 people were killed when the Omagh bomb exploded in 1998
The case against Sean Hoey, who has been cleared of 56 charges including the murders of 29 people in the Omagh bomb attack, was essentially built on forensic evidence - in particular DNA.

The Forensic Science Service (FSS), told Mr Justice Weir they had found the defendant's DNA on items relating not just to the Omagh bombing but several other bomb scenes as well.

The FSS claimed to have found Mr Hoey's DNA using a technique they had developed themselves, called Low Copy Number (LCN) DNA.

It allows DNA profiles to be uncovered even when there is only a tiny amount of DNA present, sometimes as small as a millionth the size of a grain of salt.

The FSS, a government-owned for-profit company that is Britain's largest forensics provider, began routinely using LCN testing in casework in 1999, and has said it was used to help convict - among others - the killers of the Swedish foreign minister Anna Lindh and the British backpacker Peter Falconio.

The FSS say they have used the technique about 21,000 times.

Despite that, there have been constant doubts within the scientific community about the merits of LCN testing, and Sean Hoey's defence team decided to attack the method, the science behind it and the conclusions that can be drawn from the results.

Doubts in court

For help, they turned to Professor Dan Krane, a DNA expert from Ohio.

Professor Dan Krane
Professor Dan Krane gave expert scientific evidence for the defence

"Low Copy Number tests are much more prone to flexible interpretation, than with the conventional tests.

"Because of its great sensitivity, there are much greater concerns about the persistence of DNA and its ability to be transferred from one article to another.

"It's just too easy for contamination to occur, or for DNA to have become associated with an article through very innocent, very old contact."

LCN DNA testing has been validated only by the FSS's own scientists, rather than by outside experts, and the defence's continual questioning of the method was aided by a test result from a failed bomb explosion in Lisburn, in April 1998, that Sean Hoey was also charged with.

When the defused device was analysed using the FSS's technique, the strongest initial DNA profile was found to be that of a teenage boy from Nottinghamshire.

The results could be ambiguous
Sheila Willis
Forensic scientist

In an attempt to bolster their case, the prosecution called Peter Gill, one of the inventors of the LCN technique. But under cross examination he said some of the results put forward by the prosecution were "valueless", and that LCN was a complex area in which there were "shades of grey".

That led Mr Justice Weir to say: "When this evidence is presented on behalf of the prosecution, no-one talks about it in terms of shades of grey. It's put forward as evidence I can rely on."

Further questions

Thursday's verdict will throw up considerable questions over the merits of LCN testing and will bolster the arguments of those who have always held reservations about the technique.

Paul Debenham, LGC Forensics
Paul Debenham from LGC Forensics has developed an alternative

Sheila Willis, head of the Irish Republic's Forensic Science Laboratory, told the BBC that they did not use LCN because "the results could be ambiguous".

Britain's second largest forensic company, LGC Forensics, have also long harboured doubts about the LCN method.

The company's head of research and development, Paul Debenham, told the BBC they had devised their own method for analysing small amounts of DNA, which he says, "not only establishes as many degrees of information as you can achieve from the Low Copy Number methodology, but in fact it has got some reduced degrees of complication that can affect some of these very high sensitivity analyses".

LGC's technique has also not been validated by outside experts - they are planning to have it scrutinised next year. But it undoubtedly raised further questions about the merits of LCN testing, questions that have allowed Sean Hoey to walk away Belfast Crown Court a free man.

The debate over Low Copy Number DNA


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