A former Garda commissioner has been accused of holding an “outrageous position” in terms of the evidence he has given to that Tribunal.
The Garda and the PSNI have both been criticised for failing to disclose details of 1991 investigations into alleged leaks of Garda documents.
They were allegedly given to the IRA in Donegal.
The tribunal is investigating claims of garda collusion in the murders of two senior RUC officers.
Chief Supt Harry Breen and Supt Bob Buchanan were murdered only minutes after they left Dundalk Garda Station in 1989.
The Dublin-based tribunal heard, for the first time on Wednesday, details of a major garda investigation into alleged garda leaks to the IRA in Donegal two years after the IRA ambush.
The tribunal was only alerted to the investigation in recent weeks when it was mentioned in the evidence of a former RUC officer, Witness 68.
The former Garda Commissioner Noel Conroy, pictured, gave evidence for a second time to the tribunal on Wednesday.
In 1991, he was the chief superintendent who led the investigation into garda leaks to the IRA.
The case was not mentioned by him when he previously evidence to the tribunal in September.
“This was a major investigation of leaks, which is effectively collusion,” asked counsel for the tribunal, Mary Laverty.
“You would expect it to be one of the first reports given to the Smithwick Tribunal.”
“Yes, it depends what information you requested,” replied Mr Conroy.
The investigation centred on how the IRA had received a 1990 Garda security circular, “fogra tora”, which outlined details of two men from Northern Ireland who were suspected of planting devices in Donegal in the late 1980’s.
One of the individuals, Ian Sproule, was shot dead by the IRA in Northern Ireland on 13 April 1991.
Demonstrating it had copies of the Garda “fogra tora”, the IRA had claimed to media in Derry that it had killed Mr Sproule.
Mr Conroy’s report had concluded it could not be established there were leaks from the Garda.
The tribunal was today shown an RUC report by Witness 68 which said he was satisfied “beyond doubt that there was a leak from the Gardai to the IRA”, said the BBC Northern Ireland.
In a heated exchange, Mark Robinson for the PSNI, asked Mr Conroy if it was the case that information might not be offered by him unless it was specifically asked for.
“Is it the first time you investigated alleged garda leaks?” asked Mr Robinson.
“Yes,” said Mr Conroy.
“Is it the only time you investigated alleged garda leaks?” asked Mr Robinson.
“Yes, to my knowledge,” said Mr Conroy.
“Why did you fail to refer to the ‘fogra tora’ case in your statement to the tribunal?” asked Mr Robinson.
“If you’re thinking I’m trying to hide something, far be it from the truth,” said Mr Conroy.
The former Garda commissioner agreed that the only reason the tribunal was hearing of the investigation was because of the evidence of Witness 68.
Mr Conroy also conceded that the investigation “probably” was relevant to the terms of reference of the Smithwick Tribunal.
Mr Robinson later described as “unfair” Judge Peter Smithwick’s criticism of the PSNI for failing to provide the RUC document before it was mentioned by Witness 68.
Counsel for the tribunal, Ms Laverty said neither the Gardai nor the PSNI had disclosed details of the investigation into Garda leaks to the IRA in 1991.
“The title is indicative that it relates to collusion, it begs the question what else is there in evidence?” she said.
The chairman of the tribunal moved to clarify that no evidence had been given as to how the Garda document had “ended up in the hands” of the IRA.
Ian Sproule was shot dead on April 13, 1991.
The IRA claimed he was a member of the UVF and later released Garda documents to a journalist in Derry which said Mr Sproule was a member of the loyalist group.
The document said Mr Sproule was wanted in connection with the planting of firebombs at premises in Letterkenny, Castlefin and Ballybofey on February 7th and 8th, 1987.