29 people including a woman pregnant with unborn twins were killed in the bombing
The Appeal Court in England has cast doubt on the expertise of a forensic scientist who challenged DNA evidence at the Omagh bomb trial.
Professor Allan Jamieson, who appeared as a defence witness for Sean Hoey, testified that low copy number DNA was unreliable.
However appeal court judges in another case have largely agreed that he is not qualified to give expert evidence.
Prof Jamieson said he would consider the judgement carefully.
Sean Hoey was acquitted by Mr Justice Weir of murdering 29 people including a woman with unborn twins in the bomb attack in County Tyrone in August 1998.
A large part of the case against him centred on low copy number (LCN) DNA evidence.
LCN allows genetic profiles of offenders to be created from very small tissue samples that have only been detectable with new techniques available since 1999.
on Mr Hoey in 2007, Mr Justice Weir accepted the argument Prof Jamieson had put forward with another scientist, that the science of low copy number DNA had not been "validated" by the international scientific community.
He said it was "unreliable" and test results were open to interpretation.
The Appeal Court in England has considered
two other cases
where LCN DNA helped secure convictions.
The opinions of Prof Jamieson were considered in the course of those appeals.
Crown lawyers there had argued that Prof Jamieson was not qualified to give expert evidence.
And the three appeal court judges largely endorsed that view.
DNA testing on very small samples is a relatively new technique
Their verdict stated that Prof Jamieson's expertise on the interpretation of DNA profiles "is limited, without any relevant first hand laboratory or research experience".
The judgement adds that it is "impossible to understand" how he had sufficient expertise to be able to give evidence in the Omagh case, "let alone to assist in the attack made in that case on the LCN process".
The judges also said that much of his knowledge of DNA and the analysis of low template DNA is based on reading scientific papers and discussion with other scientists, as opposed to carrying out laboratory research himself.
The Omagh bombing trial was the first case in which Prof Jamieson had provided an expert opinion on low template DNA.
Before then he had known of LCN as a process, but that case was the first opportunity he had to study it, the judges stated.
They also acknowledged that Prof Jamieson had given evidence in so many low template DNA cases since the Omagh trial that he has "acquired a degree of experience" from these cases.
However they said they "retain clear reservations about the extent of his expertise in relation to DNA profiles."
In a statement, Prof Jamieson, who has a PhD from the Forensic Science Unit at Strathclyde University, stressed that in the Omagh trial his evidence had been specifically concerned with the "validation" of the LCN process.
He said: "As repeated by the court in the trial of Mr Hoey, validation is the process by which the scientific community acquires the necessary information to a) assess the ability of a procedure to obtain reliable results b) determine the conditions under which such results can be obtained c) define the limitations of the procedure.
"As a senior member of the scientific community, I delivered my opinion regarding the deficiencies in the validation process for LCN.
"These deficiencies were considered by the court, and by many scientists in this and other jurisdictions, serious enough to warrant further investigation.
"They were not the basis upon which the verdict was delivered. They continue to be debated in the scientific community."
From 1995 until 2002, Prof Jamieson was head of Lothian & Borders Police Forensic Science Laboratory.
In 2002 he established an organisation in Glasgow with the name
The Forensic Institute.
It is a private commercial organisation and is not accredited by the United Kingdom Accreditation Service or any other body in England and Wales or Scotland.