The officer, identified only as Witness 41, served for several years along the border in South Armagh in the late 1970s and early 1980s, as a chief inspector and deputy subdivision commander.
He was transferred out of the area following a mortar attack on Newry RUC station in 1985.
“Nine people were killed in front on me,” he recalled.
“I was in the room with the nine,” he added.
“I was blown out of the canteen.”
On another occasion, he described how he and his colleagues came under fire after an IRA unit opened fire on them following the remote contrlled detonation of a roadside bomb.
“We returned fire, and they ran away,” he said.
Witness 41 said he knew chief superintendent Harry Breen since he was a childhood, when the officer served as a constable in his home town.
The tribunal is examining allegations that a leak from Dundalk garda station led to the IRA ambush in which Breen and his colleague superintendent Bob Buchanan were killed on 20 March 1989.
Because he knew the family, he was sent to deliver the news of her husband’s death to Mrs Breen.
“There used to be a programme, I think it was ‘Neighbours’,” he recalled. “I could hear the music, she came out with a cup of coffee in her hand.
A senior Garda detective has told the Smithwick tribunal he believed a former sergeant who implicated a colleague in an operation to obtain false passports which ended up in the hands of the IRA.
Detective inspector Gerard McGrath was one of the officers who interviewed former sergeant Finbarr Hickey about passport applications he signed in 1998.
Hickey, who later pleaded guilty in the Special Criminal Court, said he sign the applications at the behest of a colleague, retired sergeant Leo Colton.
When arrested and questioned, Colton described the allegation as “codswollop” and said Hickey was “away with the fairies”. He was never charged with any offence.
“I did believe Finbarr Hickey. I believed he was telling the truth chairman,” detective inspector Gerard McGrath told the tribunal.
“I believe he [Hickey] was upset, he was embarrassed, that’s what I remember,” McGrath added.
Detective inspector McGrath said the assessment was made based on his years of experience as a detective.
Barrister Michael Durack, representing the garda commissioner, said that individuals in some of the passport photos, who could not be identified, had disguised themselves, wearing glasses and facial hair to alter their appearance.
The tribunal is looking at claims that a garda tip-off allowed the IRA to set up an ambush in which chief superintendent Harry Breen and superintendent Bob Buchanan died on 20 May 1989, as they returned from a meeting in Dundalk Garda station.
Colton and Hickey, along with another former garda sergeant Owen Corrigan, deny they ever leaked information from the Garda Station.