Key question at the very heart of collusion inquiry
One of the crucial questions the Smithwick Tribunal sought to answer was: why were the IRA so confident that the two officers would be travelling along the Edenappa Road on the afternoon of Monday, March 20, 1989?
The inquiry heard that on the day of the murders, the meeting in Dundalk between the RUC officers and their Garda counterparts had been organised just that morning, yet by around 3.50pm, the IRA had mobilised up to 70 operatives, covering the three main border crossings from Dundalk into Northern Ireland.
It also heard that the south Armagh IRA were notoriously cautious and had been known to cancel an operation if even one car that they had not been expecting passed by.
The IRA claimed their attention had been drawn to Supt Buchanan's red Vauxhall Cavalier after it had been seen crossing the border some eight times in January 1989.
However, the tribunal heard evidence that on the day of the murders, the IRA had been communicating by CB radio, and that their radio activity had started at 11am – before Supt Buchanan's car had even left his driveway in Moira.
Three members of the Garda were named by the tribunal. They were retired Detective Sergeant Owen Corrigan, Sergeant Leo Colton and Sergeant Finbarr Hickey. All three have consistently denied allegations of collusion, while Mr Corrigan has successfully defended his good name in libel proceedings.
Among some of the other evidence heard at the tribunal included a claim by former Garda Chief Superintendent Tom Curran that he had gone to then Assistant Garda Commissioner, Eugene Crowley, in 1987 with concerns about Mr Corrigan.
However, he said that while he spoke, the assistant commissioner never lifted his eyes from a file he was reading.
Mr Corrigan was also alleged to have been passing information to the IRA in a 1985 RUC intelligence document known as a SB50, which was shown to the tribunal.
The former detective has strenuously denied all the accusations against him and told the tribunal that he was at the forefront of the fight against the IRA.
He told the tribunal that it was "well known to everyone in the border area" that the IRA did not need a mole to tell them the officers were in Dundalk Garda station on the day of the ambush.
Judge Smithwick concluded that while there was some evidence that Mr Corrigan passed information to the IRA, he was not satisfied that the evidence was strong enough to state that he colluded in the fatal shootings of Mr Breen and Mr Buchanan.