RTÉ's Richard Dowling reports on the background to the Smithwick Tribunal.
In the early afternoon of 20 March 1989, Chief Supt Harry Breen and Supt Bob Buchanan arrived into Dundalk Garda Station.
For Supt Buchanan, this was a frequent occurrence as he was a regular visitor to garda stations along the border as part of his job. For Supt Breen, it was an unusual occurrence.
They were there to discuss a joint operation against a well-known local republican. The meeting ended at about 3.30pm and the two officers left.
There were three possible routes they could have taken. On that afternoon, they drove up the Edenappa Road having turned off the main Dublin to Belfast road.
The road had been blocked in what had appeared to be a vehicle checkpoint.
Civilians there were ordered out of their cars and told to lie on the ground by the IRA.
As the RUC officers drove up the road, several men jumped out of a white van and started shooting.
Supt Buchanan tried to reverse his red Cavalier car but it got stuck in a ditch. He was shot dead behind the steering wheel.
Chief Supt Breen got out of the car and attempted to surrender but was shot. The final shots were fired into his head as he lay on the ground.
The IRA men then sped away cheering.
Immediately, the issue of collusion arose.
Throughout the Troubles there have been a number of controversial killings where it was claimed the police or army assisted the murderers.
While most of these related to deaths in Northern Ireland, there have also been claims that gardaí were involved in alerting the IRA to possible targets.
These include the murders of Lord and Lady Gibson in a huge roadside bomb just seconds after crossing into Northern Ireland from the Republic.
Their deaths were investigated by retired Canadian High Court Judge Peter Cory, who concluded there was no evidence of collusion by a member of An Garda Síochána.
However, he looked at other deaths and said tribunals should be set up to examine them.
All except one were in the North and involved the murders of solicitors Pat Finucane and Rosemary Nelson, as well as Billy Wright among others.
The one Tribunal he suggested the Government set up was to investigate if there was collusion in the murder of Chief Supt Breen and Supt Buchanan.
This was based on intelligence given to him by the RUC and claims made by 'Kevin Fulton', who said he was a British undercover agent working in the IRA.
He claimed gardaí had tipped off the IRA about the officers' visit, allowing them time to set up the ambush.
That led to the establishment of the Smithwick Tribunal, presided over by retired judge Peter Smithwick.
13 August 1956: Bob Buchanan joined the RUC. He was married to Catherine and they had two children, William and Heather.
5 May 1957: Harry Breen joined the RUC. Married to June, they had two children, David and Gillian.
1958: Leo Colton joined An Garda Síochána.
1963: Owen Corrigan is posted to Dundalk Garda Station where he would spend almost all of his career before retiring in the late 1980s.
1980: Finbarr Hickey joined An Garda Síochána.
20 March 1989: The IRA ambush the car carrying the two RUC officers. Supt Bob Buchanan is shot dead behind the wheel of the car.
Chief Supt Harry Breen was shot after he got out of the car and apparently attempted to surrender. Already injured, he was shot in the back of the head as he lay on the ground.
21 March 1989: Both Garda Commissioner Eugene Crowley and RUC Chief Constable, Sir John Hermon refute media allegations of a garda mole being involved in alerting the IRA to the RUC men’s visit to Dundalk Garda Station as does the president of the RUC Superintendent’s Association, the late Supt Patrick McCullagh who dismissed it as "uninformed and at best mischievous".
21 March 1989: Then RUC Sgt Alan Mains, who had been staff officer to Chief Supt Breen, made a statement that just before he left for the meeting in Dundalk, Chief Supt Breen expressed concerns that a garda in the station there was in the pay of a well known republican known as 'Slab' Murphy.
22-23 March 1989: Garda Assistant Commissioner Edward O'Dea conducts investigation in Dundalk Garda Station to establish who knew of the arrival of the two RUC officers earlier that week.
It concludes there was no leak from any garda about the RUC men’s visit.
17 April 1989: Commissioner Crowley informs the Department Of Justice, based on the O'Dea report, there was no leak from Dundalk.
6 June 1989: British army intelligence analysis of vehicles, known as 'Vengeful', concludes two cars were seen following Supt Buchanan on a number of occasions, including one linked to a member of PIRA.
1996: Now retired Owen Corrigan is abducted along with another man from the Boyne Valley Hotel in Drogheda by the IRA. They are held for two days and assaulted before being released.
November 1999: Journalist Toby Harnden’s book, Bandit Country, is published. It makes claims about collusion in a number of murders, including Breen and Buchanan.
10 March 2000: A column by Kevin Myers appears in the Irish Times repeats the allegation of collusion in the Breen and Buchanan murders but also in a number of other killings.
25 March 2000: David Trimble MP, MLA writes to then Taoiseach Bertie Ahern demanding an inquiry.
13 April 2000: Jeffrey Donaldson MP, using parliamentary privilege, names a retired gardaí as the IRA mole and called for the establishment of a Tribunal.
13 April 2000: as a result of parliamentary questions, then Minister for Justice John O'Donoghue, announces he has asked the Garda Commissioner to investigate claims of collusion again but said "no tangible evidence" had been uncovered previously to back up such claims.
The investigation carried out by Detective Chief Supt Sean Camon and Det Insp Peter Kirwan concluded there was no evidence to suggest there was collusion in the murder of the two RUC officers.
2001: Finbarr Hickey sentenced to jail for signing false passport papers, some of which ended up in the hands of the IRA
August 2001: As a result of the Weston Park Agreement both governments agree to investigate a number of controversial killings where collusion has been alleged. The murder of Pat Finucane, Rosemary Nelson along with Supts Breen and Buchanan as well as others, are to be probed.
May 2002: Retired Canadian High Court judge, Peter Cory begins his investigation into a series of murders.
December 2003: Publication of the report by Judge Cory which recommended the establishment of an inquiry into the murders of Supt Buchanan and Chief Supt Breen.
March 2005: The Oireachtas agrees to set up a Tribunal of Inquiry at the request of the then Minister for Justice, Michael McDowell.
Its terms of reference is to inquire into suggestions that "members of An Garda Síochána or other employee of the State colluded in the fatal shootings..."
Mr McDowell said the inquiry would be completed in "as economical a manner as is possible and at the earliest possible date, consistent with a fair examination of the matters referred to it."
February 2006: Smithwick Tribunal retains counsel and offices.
March 2006: The Tribunal holds its first public hearing before adjourning to begin its investigative phase of work.
June 2011: The Tribunal begins hearing evidence in public.
21 June 2013: The final sitting of the Smithwick Tribunal takes place.
29 November 2013: The final report of the Tribunal is given to the Clerk of the Dáil.