Buchanan was killed outright whilst Breen, suffering gunshot wounds, was forced to lie on the ground and shot in the back of the head after he had left the car waving a white handkerchief.

This led to the Irish government setting up the Smithwick Tribunal, a judicial inquiry into the killings which opened in Dublin in June 2011 and published its final report in December 2013.

In the Judge Peter Smithwick report he was unable to find direct evidence of collusion but said 'on balance of probability', somebody inside the Dundalk Garda station had passed on information to the IRA regarding the presence of Breen and Buchanan.

[9] The two RUC officers were travelling without escort in Buchanan's personal unmarked car: a red Vauxhall Cavalier with the registration number KIB 1204 which was not armoured-plated and did not have bullet-proof glass.

[12] According to the Cory Collusion Inquiry Report, as Buchanan reached the hilltop he was flagged down by an armed IRA man standing in the middle of the road wearing Army battle fatigues and camouflage paint on his face.

[7][13][14] After removing security documents relevant to the meeting with Garda from the Cavalier and personal belongings of the two officers including notes for a history of his church Buchanan had been writing, and a diary containing the contact details of informers and an RUC assistant Chief Constable (whose house was later bombed) from Breen, the IRA gunmen drove away from the scene of the killings.

Police arrived on the scene at 3.54 pm, where they found Breen lying dead on the roadside; alongside the body was his pen, his glasses and the white handkerchief that he had been carrying.

[1][2] In a House of Commons parliamentary debate held the day after the killings, unionist politicians, many of whom had been personally acquainted with Breen and Buchanan, criticised the decision to send the unarmed officers to a meeting in Dundalk, a town renowned at the time for its close IRA affiliations.

He appeared on television in May 1987 holding a press conference following the Loughgall Ambush in which the Special Air Service shot dead eight IRA members.

[2] Judge Cory remarked that he was dedicated to the protection of the public and was concerned for the welfare of the RUC officers who served under his command which was an attribute greatly appreciated by them.

At the Smithwick Tribunal more than twenty years after his death, several former Garda officers testified they had come to regard him as a personal friend as he frequently visited their stations in his capacity as Border Superintendent.

[19]: 216–221  Buchanan had raised with Gardaí in Monaghan in 1987 that the RUC were concerned about the same Garda officer was 'unduly associating with the IRA' and hours before he left Armagh police station to meet Buchanan at Newry station, Breen had confided to Staff Officer Sergeant Alan Mains that he had a sense of foreboding about his trip to Dundalk because he believed the same Garda was in the pay of a senior IRA man living on the Armagh/Louth border and would pass on information to him.

He reportedly had never been worried about his safety whilst driving unarmed through the staunchly republican, IRA-dominated south Armagh countryside as he believed that "God would protect him".

[13] In March 2000, several months after the publication of Harnden's Bandit Country book,[19] journalist Kevin Myers wrote in the Irish Times about the allegations of collusion between a Garda mole and the IRA, stating that they had led to the deaths of Breen and Buchanan.

David Trimble MP for Upper Bann, MLA (and future First Minister of Northern Ireland) then wrote a letter to the Taoiseach Bertie Ahern TD on 25 March 2000, calling for an inquiry into the allegations of collusion.

[26] Jeffrey Donaldson, MP for Lagan Valley, used his parliamentary privilege in the House of Commons on 13 April 2000 to suggest that the named Garda detective sergeant passed on information to the IRA about the meeting in Dundalk which facilitated their ambush of the RUC officers.

[9] The two policemen were also unaware that a British Army surveillance team had watched and noted IRA "dickers" following Buchanan's car but had failed to warn RUC Special Branch of this.

Before the public hearings began, members of the Smithwick Tribunal's legal team met with three former senior IRA volunteers, one of whom had a command role in the operation to kill the two officers.

Curran—who had met Buchanan many times and regarded him as a friend—was worried and duly informed Eugene Crowley, the assistant commissioner of crime and security at Garda headquarters in Dublin, about the threat.

[7][26] Retired Garda Detective Sergeant Sean Gethins told the Tribunal that the IRA team at Jonesborough had initially planned to kidnap and interrogate Breen.

[37] Kevin Fulton suggested British agents who took part in the ambush at Jonesborough had shot Breen and Buchanan lest they reveal the names of informants whilst under torture.

[26] It was there that Secretary of State for Northern Ireland Tom King had suggested the meeting after receiving reports from a British Army colonel about the cross-border smuggling activities of a well-known IRA man whose property straddled the Armagh/Louth border.

According to Sgt Alan Mains, Breen was "specifically directed to speak with the Guards [Gardai] and the Army, and to come up with some kind of reply for the Chief Constable and the Secretary of State".

[2] A former RUC Special Branch chief, however stated to the Tribunal that both Breen and Buchanan had been opposed to carrying out "Operation Amazing" against the smuggler as there was not enough substantial information on which to base it.

Civilians Robert and Maureen Hanna, along with their seven-year-old son, David, were killed when the IRA team detonated a 1,000-pound landmine as their jeep drove past, having mistaken their vehicle for that of Judge Eoin Higgins.

[49] "Witness 62" added that on the day of the Jonesborough ambush, the IRA had placed a "spotter" on the road from Dundalk to observe which direction Breen and Buchanan would take to return north.

[54] Weir was a prominent member of the Glenanne gang, a loose alliance of loyalist extremists which included the UVF Mid-Ulster Brigade and rogue elements of the security forces.

[55] Investigative journalist Paul Larkin, in his book A Very British Jihad: collusion, conspiracy and cover-up in Northern Ireland, claimed that Breen was a leading officer in the SPG.

[56] Judge Peter Cory stated in his report that the Provisional IRA had developed sophisticated intelligence-gathering techniques which enabled them to monitor the telephone calls and radio transmissions of the RUC and British Army.

He maintained that the IRA was too professional an organisation to have attempted an ad hoc ambush on such short notice as would have been the case had the attack been carried out upon being alerted by a Garda mole as to the presence of the two senior RUC officers at the Dundalk station.