The Saville Inquiry sat in London for most of 2003, hearing evidence from soldiers who said they could not come to Derry because of fears for their safety.
Among them was Soldier F, who admitted killing Michael Kelly, Barney McGuigan and Paddy Doherty and an unidentified man, who may have been William McKinney.
The former Prime Minister, Sir Edward Heath, also gave evidence, but denied pressurising Lord Widgery into exonerating the soldiers who fired the fatal shots.
The inquiry returned to Derry in October.
Documents released under the 30-year-rule at the start of the year revealed that Mr Heath, was warned days before Bloody Sunday that soldiers sent to the city had already "over-reacted" at civil rights protests.
In a conversation with Lord Widgery, the prime minister warned him not to forget Britain was fighting a propaganda war as well as a military one.
When questioned about this statement, he told the inquiry there had been "nothing sinister" in his comments.
Asked by a barrister whether innocent people were murdered on Bloody Sunday, he refused to answer, and said he had not made a statement at the time and would not do so now.
He also refused to apologise to the families of those killed on the grounds that he had already expressed intense regret at the time.
The former prime minister rejected suggestions that government policy was to send troops into the Bogside, that troops were authorised to shoot troublemakers to control crowds and that any blame for casualties was intended to be placed on to the organisers and the gunmen.
He said he never promoted or agreed to the use of unlawful lethal force in Northern Ireland, and said suggestions that the British government planned the events of Bloody Sunday were "absurd".
The inquiry also heard evidence which challenged claims that Gerald Donaghy had been carrying nailbombs when he was killed.
Photographs taken at an army checkpoint after Mr Donaghy's death showed nailbombs in his pockets, but his family said these were planted by the army.
Leo Young, whose brother John was killed on Bloody Sunday, said he carried Mr Donaghy's body to a house, searched his pockets, and then travelled with him in a car to an army checkpoint.
"If there had been nail bombs in his pocket I would have seen them," said Mr Young.
The former soldier who drove Mr Donaghy's body from the army checkpoint to a military compound at Craigavon Bridge also said he did not see any nailbombs at the time.
Soldier 150 said he certainly would not have driven the car if there had been nailbombs on Mr Donaghy's body.
Role of the Army
A former army commander told the Saville Inquiry that he was "very annoyed" when he learned the Parachute Regiment was to be used to arrest rioters on Bloody Sunday.
Colonel Roy Jackson, who was in charge of the Royal Anglians, said he told the soldier in charge of the operation that the Paras should not be used as they did not know the Bogside area.
Colonel Jackson said Brigadier Pat MacLellan replied that he could not change anything as the decision to use the Paras had been made at the highest level.
But the soldier in charge of the parachute regiment, Colonel Derek Wilford, rejected suggestions he ordered a full frontal assault on the Bogside.
Colonel Wilford said that when he sent the company of Paras into the Bogside in armoured cars they were still part of a pincer movement that he had always planned.
Colonel Wilford agreed that the plan changed significantly on the day but said this had to happen as the rioters had run back into the Bogside.
He defended the actions of his troops, saying he believed his men could have done nothing better on the day.
One of the soldiers, Soldier F, was told he faces allegations of murdering at least four people on Bloody Sunday.
He agreed he killed four people, but insisted he did not murder them, and said he fired only at a gunman and two nailbombers.
He admitted killing Michael Kelly, Barney McGuigan and Paddy Doherty and an unidentified man, who may have been William McKinney, in Glenfada Park.
Role of the IRA
Five former Official IRA men told the Saville Inquiry they fired three shots in the Bogside on Bloody Sunday.
One of the men said he fired one rifle shot when he realised Damien Donaghy and John Johnston had been shot.
He said he then put the rifle into the boot of a car, where it stayed during the Army operation.
A second man told the inquiry he was near the Rossville Flats when the Army came into the Bogside and started shooting.
He said he fired two shots from a pistol at soldiers in armoured cars and got out of the area quickly.
This gunman was seen by the now retired Bishop of Derry, Dr Edward Daly, who told him to "clear off".
The five former Official IRA men said they were certain no other members fired shots while the paratroops were in the Bogside, but they said another member was wounded in an exchange of fire outside the area and after the main shootings had ended.
Martin McGuinness also gave evidence to the inquiry, but refused to identify the IRA's officers in the city on Bloody Sunday.
He said he would "rather die" than "betray" other IRA members by naming them.
But he did tell the inquiry that the Derry commander of the Provisional IRA on the day was still alive and well, but he did not know why he had not come forward to give evidence.