Lord Saville and his colleagues have been sifting through a vast amount of evidence in order to answer key questions about the events of Bloody Sunday.
The inquiry set out to establish the truth about what happened in Londonderry on 30 January 1972.
The final report being published on Tuesday is expected to provide answers to many outstanding questions:
- Were those killed and injured all unarmed and innocent civilians?
- Why and how did the Paratroop Regiment soldiers fire the fatal shots?
- What orders were given by their commanding officers?
- Did the soldiers shoot in response to IRA gunfire?
- Who fired the first shots?
- Was the government prepared to sanction a shoot-to-kill policy to reclaim "no-go" areas such as Derry's nationalist Bogside area?
BBC News lays out some of the key issues to be addressed in the report.
Relatives of those killed on Bloody Sunday want Lord Saville to give official recognition they were unarmed and innocent civilians, who were unlawfully killed.
The initial government inquiry, which released its findings weeks after the shootings, concluded "there was no reason to suppose" the soldiers would have opened fire without being attacked first. That report, by Lord Widgery, was widely regarded as a whitewash.
- Were any of those killed or injured carrying weapons? Gerald Donaghy was photographed at an Army post with four nail bombs in his pockets but a number of civilians, who tried to take him to hospital, told the tribunal that he was not armed and the bombs were planted on him by the Army;
- Were the victims unlawfully killed? The inquiry heard some of them were shot in the back;
- Was anyone other than the known dead and wounded shot? Lawyers for the soldiers claimed gunmen were killed on Bloody Sunday and their bodies were spirited away.
A key question for the tribunal is whether individual soldiers broke the law.
They face allegations that they either murdered people, fired without justification or gave false evidence.
- Were they justified in shooting because they were fired upon first? They say they acted in self-defence and only fired at IRA gunmen and nail bombers;
- Were the shots fired indiscriminately?
- Which soldiers fired the fatal shots?
- If Lord Saville finds the shootings were unlawful, will he suggest that prosecutors consider charges of manslaughter or murder? Soldiers who appeared as witnesses were not granted immunity from prosecution; only immunity from self-incrimination. It is possible that individual soldiers could be prosecuted for their role in Bloody Sunday, but in practice this is highly unlikely.
Senior British army officers
The inquiry will try to establish what orders were given to the soldiers on the day.
A number of senior army officers testified in London, including the soldier in charge of the Parachute Regiment on the day, Colonel Derek Wilford, and the soldier in charge of the whole operation on Bloody Sunday, Brigadier Pat MacLellan.
- What were the orders given to the Paratroops?
- Was there a breakdown in communication? Colonel Wilford said his soldiers knew what was expected of them. He said he believed his troops were shot at and returned fire within the rules of engagement, and he saw or heard nothing which led him to believe that paratroops were out of control at any stage.
- Were they in full control of their men or did the soldiers disobey orders by opening fire? Brigadier MacLellan said it appeared that the paratroops disobeyed his orders by driving right into the Bogside in armoured cars. However, Colonel Wilford rejected this and insisted there was nothing to stop him going into the Bogside.
- Did they cover up the events of the day?
The Official and Provisional IRA
Central to the soldiers' explanation of events is the claim they were responding to IRA gunfire.
Martin McGuinness was the most prominent former IRA man to give evidence to the tribunal.
The Sinn Fein MP, who is Northern Ireland's Deputy First Minister, admitted he was the IRA's second-in-command in Derry at the time. He was urged by the tribunal to name other IRA members but he said he would "rather die" than "betray" them.
A number of other former IRA members gave evidence; some of their identities were kept secret.
- Did any IRA units take part in the march? Mr McGuinness said this was not true. He said armed IRA members were standing by in the Creggan and Brandywell areas during the march, but that it had been agreed by the organisation in advance that the city should be peaceful to facilitate a protest peaceful march.
- Did a republican gunman fire the first shots?
- Did IRA gunmen fire shots at British soldiers? Colonel Ted Loden, the major in charge of a Parachute Regiment unit that fired more than 100 shots, said no-one would have died on Bloody Sunday if the IRA had not tried to murder soldiers. The inquiry heard that the Official IRA had fired six shots - but not until the army had started shooting.
- Were IRA activists carrying nail bombs, as alleged in soldiers' evidence? Former Provisional IRA Michael Clarke told the inquiry he was certain nail bombs were not used on Bloody Sunday. He said he was an explosives officer and that no-one asked him for explosives or detonators.
- What did Mr McGuinness do on that day? The inquiry heard Mr McGuinness shot at the Army, possibly sparking the violence; he dismissed the claim as a "pathetic fabrication".
The shootings happened against a backdrop of worsening violence in Northern Ireland; the march was a protest against internment - a form of imprisonment without trial introduced at the height of the political and civil crisis.
Then-prime minister Sir Edward Heath, who gave evidence to the Inquiry in January 2003, was warned by a senior official days before Bloody Sunday that soldiers being sent to the city had already "over-reacted" at civil rights protests.
In the aftermath, he told the then-Lord Chief Justice Lord Widgery, who led the 1972 government inquiry: "It had to be remembered that we were in Northern Ireland fighting not only a military war but a propaganda war."
- Was the Army told it was legal to use lethal force in certain situations? The inquiry heard then-chief of staff Lord Carver had been told by Mr Heath he had been advised it would be lawful for British troops to shoot anyone who got in the way. This was rejected by Mr Heath.
- Were the killings part of a high-level conspiracy by the governments in Westminster and Belfast in order to take back "no-go" areas like Derry's Bogside? Mr Heath rejected this, saying the operation was seen as very much one of containment.