An official report for the British government carried out by a former Appeal Court judge has rejected allegations that vital intelligence about the Omagh bomb attack had been held back.
Intelligence Services Commissioner Sir Peter Gibson said any information on the bombers taken from telephone intercepts obtained by the electronic monitoring station, GCHQ, was passed to the RUC Special Branch but could not have prevented the August 1998 atrocity.
Mr Gibson also said there was no evidence before him that gardaí had warned the RUC of a likely attack.
29 people, including a woman expecting twins, were killed when a Real IRA car bomb exploded in the Co Tyrone town in August 1998.
No one has ever been convicted of the attack.
Peter Gibson was called in by British Prime Minister Gordon Brown after claims that GCHQ withheld intercepted intelligence about the bombers' movements on the day of the explosion.
Mr Brown, who is to meet some of the victims' relatives at Downing Street next month, is expected to face fresh demands for a full cross-border judicial inquiry into the outrage.
Even though the families are involved in a multi-million pound High Court compensation claim against the five men they allege were responsible for the attack, they still want the British and Irish governments to agree to an inquiry.
The court case in Belfast began last April and is due to end with closing submissions in March.
Northern Ireland Secretary Shaun Woodward said the British government shared the public's deep regret that the bombers had not been brought to justice.
A BBC Panorama programme had claimed that intelligence officers had tracked the movements of the bombers' car and a scout car on their way to Omagh from the Republic on the day of the attack.
However, Mr Gibson said technology was not advanced enough in 1998 to do that.
PSNI Chief Constable Hugh Orde said he accepted the conclusions.
This evening, the BBC says in a statement that it stands by the Panorama programme.
'Both the programme and Sir Peter Gibson's report raise many new questions of significant public interest about what happened before the Omagh atrocity and in the aftermath,' the statement says.