Sergeant Lionel Mullaly said he was told to look for mention of retired detective sergeant Owen Corrigan by Peter Kirwan, now a detective chief superintendent. Mullaly worked in Crime & Security, the Garda security and intelligence section, at the time.
Mr Corrigan is one of three former sergeants represented before the Smithwick tribunal, set up to look at allegations of garda collusions in the 1989 IRA killings of two senior RUC officers, chief superintendent Harry Breen and superintendent Bob Buchanan, as they returned from a meeting in Dundalk Garda station.
Mr Corrigan denies any allegations of collusion, and has described them as a “monstrous lie”.
Sergeant Mullaly said he was asked to look at all intelligence reports relating to the murders of Lord Justice and Lady Gibson, the Hanna family, and the two RUC officers.
Mr Kirwan, at the time a detective inspector in the intelligence section, was assigned to the inquiry to act as a Crime & Security liaison with detective chief superintendent Sean Camon, who headed the internal Garda probe.
The intelligence review took place following the publication of Bandit Country by journalist Toby Harnden, alleging garda collusion in a series of IRA attacks in the late 1980s, and an article on the same topic by columnist Kevin Myers.
Questions were also raised in the Dáil and the House of Commons about the allegations.
Sgt Mullaly said he was not asked to look for intelligence reports referring to phone tapping activities by the IRA.
And he was not given the name of any other garda during his search of the files.
The Camon/Kirwan report found no evidence to support the allegations of collusion.
Earlier Mr Kirwan, who gave evidence to the tribunal in December, was recalled to give evidence about an intelligence file in Garda HQ.
He said an earlier report counterbalanced a 1991 report discussing inappropriate contacts between detective sergeant Corrigan and a car shop owner with a previous IRA-related conviction.
Tribunal barrister Mr Justin Dillon SC said the report was so sensitive it could not be summarised for the tribunal, but the tribunal chairman was aware of the report’s contents.