RETIRED garda sergeant Leo Colton was trusted by Provos and helped members get their hands on false passports, the Smithwick tribunal found.
Judge Peter Smithwick said Mr Colton assisted the Provisional IRA in 1995 and 1996 by having his former colleague, Finbarr Hickey, sign false passport applications.
"This is a relatively significant form of assistance and suggests to me that members of the Provisional IRA reposed considerable trust in Mr Colton at that point," the judge said.
But he added he did not think there was sufficient evidence to establish there was a relationship between Mr Colton and the Provisional IRA as far back as 1990.
Hickey was jailed for his part in the passport scam, but argued he only did it because Mr Colton had asked him to, not knowing they were counterfeit.
Some ended up in the hands of known IRA men.
Mr Colton was never charged or convicted and has always denied the allegation, despite several senior officers - including Commissioner Martin Callinan - telling the tribunal they believed Mr Hickey's version of events.
Mr Colton also claimed blank passport and driving licence forms found at his home during a garda search were there in case neighbours asked him for help in filling out forms.
The retired officer maintained he "never had many dealings" with the IRA during his work along the border over three decades.
He was on duty in Dundalk on March 20, 1989, the day Chief Superintendent Harry Breen and Superintendent Bob Buchanan were ambushed, but insisted he did not know the RUC members were meeting his superiors.
He branded suggestions he used hand signals to notify the IRA of the presence of RUC officers at the garda station as "ridiculous".
He instead told investigators he spotted a grey car drive slowly past the front of the station that afternoon, as if the driver was looking at the cars parked in the area.
Mr Colton joined the force in 1958 and was stationed in Co Donegal, first in Buncrana and then Letterkenny.
Seven years later he was promoted to sergeant and transferred to Ballinrobe in Co Mayo and on to Dundalk, Co Louth.
Personnel records from when he went for the promotion found him "well conducted, efficient, friendly".
Mr Colton resigned in 1991 days before a disciplinary inquiry was due to be held against him over the issuing of a trade plate - a registration used by traders for unlicensed cars - to a known IRA member. He said the timing was a coincidence.
The former officer had written a recommendation for Dundalk man Brian Ruddy who had a conviction for possession of the illegal animal growth promoter Angel Dust, and was believed to have "potential associations with subversives".
Judge Smithwick said he did not accept Mr Colton's evidence that he knew nothing of Mr Ruddy, including his background, conviction or criminal associations, when he certified that he was eligible for a trade plate.
"The evidence of a direct connection with the Provisional IRA is not, however, as clear in relation to this incident," the judge added.