The Smithwick Tribunal into the murders of Chief Superintendent Harry Breen and Superintendent Robert Buchanan opened in Dublin yesterday.
On March 20, 1989, the two men travelled to Dundalk Garda Station for a meeting with a senior garda officer which had been arranged only that morning. On their return across the border, they were ambushed and killed by the IRA on the Edenappa Road in Co Armagh. There have long been claims that the IRA was tipped off about their return route by a member of the gardaí.
Reading his opening statement yesterday, the tribunal's sole member, Judge Peter Smithwick, said he would examine the issue of collusion in the broadest sense.
"While it generally means the commission of an act, I am of the view that it should also be considered in terms of an omission or failure to act," he said.
"In the active sense, collusion has amongst its meanings to conspire, connive or collaborate. In addition, I intend to examine whether anybody deliberately ignored a matter, or turned a blind eye to it, or pretended ignorance or unawareness of something one ought morally, legally, or officially oppose."
The tribunal was established by the Government following a recommendation from retired Canadian Supreme Court judge Peter Cory, who investigated six allegations of collusion between Irish and British security forces and paramilitaries, one of them being the murders of officers Breen and Buchanan.
While Judge Cory found the IRA had not necessarily needed information from the Garda to mount its 1989 ambush, there were two intelligence reports which referred to such a leak.
In addition, a man known by the pseudonym Kevin Fulton, said to be a former British intelligence agent who had infiltrated the IRA, had given a statement in which he also alleged collusion. Combined with the intelligence reports, Judge Cory believed there were sufficient grounds to recommend a tribunal be established.
But at the tribunal's first sitting yesterday, a barrister representing a former garda vehemently denied allegations that his client had colluded in the killings.
Former detective sergeant Owen Corrigan retired from the force in 1991 and could be of "no assistance" to the tribunal, barrister Jim O'Callaghan said.
But Mr Corrigan had been "dragged into" the matter by unionist MEP Jeffrey Donaldson, who alleged under parliamentary privilege in the House of Commons in 2000 that the former garda had been involved.
"That statement by Jeffrey Donaldson was a monstrous lie," Mr O'Callaghan told the tribunal.
The barrister applied for legal representation at the tribunal on behalf of Mr Corrigan, who was not present.
The families of both Mr Buchanan and Mr Breen also made applications for legal representation.
Judge Smithwick will adjudicate on those applications shortly.