Former Northern Ireland police chief Sir Ronnie Flanagan has been urged to participate in a cross-Border independent inquiry into the Omagh bombing inquiry.
Michael Gallagher, whose son Aidan was among 29 people killed in the 1998 Real IRA attack, said a cross-Border inquiry was needed to focus on failings in investigations into the attack.
Speaking from a conference for victims of terrorism across the world in Madrid, Mr Gallagher said: "There have been serious failings at all levels on both sides of the Border and the only way to address all these issues is through a comprehensive independent cross-Border public inquiry rather than having them raised in a piecemeal fashion.
"Sir Ronnie is someone who could bring a lot of knowledge and help to an independent inquiry, and I would hope he would freely go and open up."
The RUC was heavily criticised by judge Mr Justice Weir after South Armagh man Sean Hoey was cleared of the Omagh murders and a series of other dissident republican attacks.
Mr Justice Weir accused the RUC of malpractice at every stage of evidence gathering procedures during the case and of "deliberate and calculated deception".
Sir Ronnie, then head of the RUC, insisted that he would not resign from his current post of chief inspector of the British inspectorate of constabulary.
When doorstepped by Channel 4 last night, Sir Ronnie at first refused to say anything but then said: "I absolutely publicly apologise to the families in Omagh. I feel desperately sorry that we have not to this point brought people to justice for that terrible attack," he said.
"I publicly apologise to all the families, and all the victims, and all those who suffered, without reservation," he added.