Former garda commissioner Pat Byrne was questioned at the Smithwick tribunal by barrister Justin Dillon SC.
Mr Byrne said that one of the three men, RUC superintendent Alan Mains, was interviewed by the RUC.
The two other men, unionist MP Jeffrey Donaldson and Fine Gael TD Charles Flanagan, raised questions about Garda/IRA collusion in the House ofCommons and the Dáil.
Mr Donaldson named a retired Garda in the Commons. Mr Flanagan told the tribunal last year he was also given a Garda’s name, but decided not to name him using Dáil privilege as he was not present to defend himself.
But Mr Byrne said there was no need for Sean Camon, the chief superintendent in charge of the collusion inquiry, to interview the two politicians.
“He knew the two names they were referring to,” Mr Byrne said.
He said that he accepted the Camon report, and in turn prepared a synopsis for the department of justice, as the original report was quite lengthy.
The investigators did interview journalist Kevin Myers, who wrote an Irish Times article about the allegations, and flew to the USA to speak with British journalist Toby Harnden, author of the book Bandit Country.
The tribunal is investigating allegations of garda collusion in the IRA ambush which killed two RUC officers in March 1989. Mr Corrigan denies allegations of collusion, describing them as a “monstrous lie”.
Mr Byrne said the Camon inquiry would have had access to any intelligence reports about garda collision held by Garda Intelligence.
But Mr Dillon said the Camon report did not refer to three intelligence reports in the years following the deaths of Mr Breen and Mr Buchanan.
Mr Byrne said it was his understanding and his belief that all the intelligence was looked at by Mr Camon in preparing his report.