The two senior officers were ambushed while returning to Northern Ireland after a meeting with Garda officers to discuss a “joint operation” on lands owned by well-known republican Thomas “Slab” Murphy.
During an opening statement, barrister Mary Laverty for the Smithwick tribunal revealed that the meeting with former Provisionals took place “in recent weeks”.
The inquiry is looking at allegations that information about the movements of Chief Supt Harry Breen and Supt Bob Buchanan was passed on to the IRA by a Garda “mole”.
The face to face meeting involved “former leadership both at national and local (South Armagh) level”, Ms Lafferty said, including one member who had a “command role” during the ambush on 20 March 1989.
Allegations of collusion first emerged within days of the ambush, and have been the subject of several Garda and RUC/PSNI investigations over the years.
But while the investigations found no evidence of collusion, an inquiry by Candian judge Peter Cory called for a tribunal to look at the case.
The tribunal has conducted hundreds of interviews with formmer and serving members of the PSNI and RUC, An Garda Siochana, politicians, and journalists.
Telecoms engineers have also been interviewed about claims that the IRA could have tapped local telephone exchanges to monitor calls about the movements of the two officers.
Other interviews took place with a former British agent identified as “Kevin Fulton”, who claimed that a former detective sergeant, Owen Corrigan, was named to him as a source of information by an IRA handler.
Mr Corrigan has denied the allegations, and other Garda and RUC probes found “no evidence” of collusion.
Tribunal barrister Mary Laverty said that if all intelligence reports were taken at face value, it would mean upp to five IRA moles were involved in planning the 1989 ambush. She emphasised that intelligence reports were not fact, and all the evidence would be weighed by the tribunal before it reached any conclusions.
And she said the tribunal’s investigation had taken so long because it had to start its inquiries from scratch, and found it “extremely frustrating” dealing with “bureaucracy” to get hold of some files.
These included documents seen by Judge Peter Cory, which had to be moved from the British Cabinet Office to a â€œsecure locationâ€ in Northern Ireland.
The tribunal will call its first witnesses to give evidence in public on Thursday (9 June).