HERE is a timeline of events of key events around the Smithwick tribunal.
:: March 20, 1989: Chief Superintendent Harry Breen and Superintendent Bob Buchanan travel to Dundalk Garda Station. On their way home they are murdered in an IRA ambush just north of the border near Jonesborough, south Armagh - two of the highest-ranking RUC officers killed in the Troubles.
:: March 22, 1989: The IRA issues a statement admitting the double murder. The terrorists claim they found confidential documents on cross-border policing in the men's car.
:: April 9, 2000: Democratic Unionist MP Jeffrey Donaldson uses parliamentary privilege in Westminster to allege a former garda detective sergeant, Owen Corrigan, colluded with the IRA in the murders. Mr Corrigan later describes it as a "shameful, monstrous and terrible lie".
:: An internal Garda investigation later that year found no evidence of collusion.
:: December 18, 2003: Canadian judge Peter Cory recommends an inquiry into the murders, along with other killings in the Troubles alleged to involve paramilitary/security force collusion. He found that the IRA might not have needed any assistance from rogue gardai and that intelligence reports made similar conclusions but he also noted reports of a garda leak about the men's visit.
:: May 31, 2005: The tribunal is formally established.
:: March 3, 2006: Judge Peter Smithwick sets out what collusion means in terms of his inquiry: "While it generally means the commission of an act, I am of the view that it should also be considered in terms of an omission or failure to act."
:: More than 200 witnesses are interviewed behind closed doors.
:: October 16, 2006: Alleged British agent Stakeknife, Freddie Scappaticci, is refused legal representation while double agent Kevin Fulton is granted representation. Fulton, also known as Peter Keeley, alleged the IRA was told by a garda officer that both RUC men were in Dundalk on the day of the ambush.
:: June 7, 2011: Tribunal lawyers reveal they have met three senior IRA commanders, one of whom had "first hand" knowledge and a "command role" in the murders.
:: The lawyers' 72-page statement says that during the meeting in Dundalk, hours before his death, Mr Breen accused Mr Corrigan of taking payments from alleged former IRA leader Thomas "Slab" Murphy.
:: June 9, 2011: An unidentified former RUC assistant chief constable claims that Mr Breen and Mr Buchanan disobeyed an order from RUC chief constable John Hermon given four days before the ambush not to cross the border.
:: June 29, 2011: Retired garda chief superintendent Tom Curran, based in Monaghan town in 1989, reveals Commissioner Eugene Crowley should have known about a death threat against Mr Buchanan between March and October 1988.
:: June 30, 2011: Judge Smithwick launches an attack on Ireland's Justice Minister Alan Shatter, accusing him of interfering with the tribunal after he controversially imposed a deadline on hearings.
:: December 16, 2011: Stakeknife sends a lawyer to the tribunal to reveal he is actively considering giving evidence. He never attends in person but is granted representation.
:: March 14, 2012: The tribunal hears allegations that a former Irish taoiseach ordered gardai not to co-operate with investigations into the IRA's 1979 Narrow Water massacre which left 18 British soldiers dead. It is claimed it was to be treated as a political crime because of what happened on Bloody Sunday. The former taoiseach was not named.
:: At the same hearing the unidentified RUC officer who made those claims, a retired former deputy assistant chief constable, also alleged garda co-operation during the Narrow Water inquiry was "beyond non-existent" and that a suspected detonation site in the Republic was destroyed.
:: April 24, 2012: Sinn Fein's Martin McGuinness is forced to deny he was involved in sanctioning the ambush of Mr Breen and Mr Buchanan. British intelligence officer Ian Hurst - also known as Martin Ingram - claimed to have inside knowledge of the terrorist attack and made the allegation.
:: May 1, 2012: PSNI intelligence states that IRA chiefs know false information is being fed to the inquiry to ensure it wraps up investigations quickly.
:: October 4, 2012: James O'Donovan, former head of the Republic's forensic state laboratory, says evidence against two suspects in the IRA ambush was quite good and he was surprised no one was prosecuted.
:: June 21, 2013: The PSNI is accused of handing over impenetrable, anonymous and unverified intelligence by lawyers for Garda Commissioner Martin Callinan. The document claimed several unnamed gardai colluded with the Provos.
:: November 12, 2013: William Buchanan, son of Mr Buchanan, rejects claims his father did not take his personal security seriously.
:: November 29, 2013: The tribunal's long-awaited report into collusion allegations is handed to the Irish parliament.