It is still unclear which soldiers shot 27 civilians on Bloody Sunday, the Saville Inquiry has heard.
The Bloody Sunday tribunal has heard from more than 900 people
Counsel to the inquiry Christopher Clarke QC said the central question was why and how civilians were killed or wounded in Londonderry in 1972.
Lord Saville is investigating the deaths of 14 civilians shot by soldiers during a civil rights march in the city in January that year.
The inquiry is now in its final phase - six years after it began.
Bloody Sunday inquiry facts
Lord Saville held his first hearing at Derry's Guildhall in April 1998.
The inquiry began to hold public hearings in March 2000
The tribunal has now sat for 433 days.
It has heard evidence from 921 witnesses.
There have been 1,555 written statements from witnesses.
The final bill will be around £150m.
The final report is expected next summer.
Mr Clarke is giving a brief summary of the evidence in a closing speech expected to last two days.
He told the tribunal on Monday: "It has to be said that, even after many days of evidence, the answer to even the first question - who shot them? - is not, on the soldiers' evidence, in any way clear."
Mr Clarke said the tribunal could take one of two views on this.
"One view that the tribunal might take is that this is something that is not
surprising if, as they say to be the case, soldiers came under fire from
unexpected quarters and had swiftly to retaliate."
The second was that the soldiers, while claiming they hit gunmen and nail
bombers, seemed unable to explain why they killed or wounded 27 people who were
"These considerations may have a cumulative effect. The tribunal may attach
some significance to the fact that so much is unexplained," he said.
"It might conclude, taking that fact with all the other evidence, that so
much is unexplained because no justifiable explanation could be given.
"On the other hand, it might take the view that uncomfortable facts have been
airbrushed out of history and that the situation the soldiers faced was
radically different to that of which the civilian evidence speaks."
Mr Clarke told the tribunal that the soldier in charge of the Army operation had no idea about the details of the Parachute Regiment plan.
He said Brigadier Pat MacLellan thought the paras were going into the Bogside on foot and did not know that they were actually driving down Rossville Street in ten vehicles.
He also said that the paras gave very little information to Brigadier MacLellan about what was happening in the Bogside.
Soldiers shot 13 people dead in Derry on Bloody Sunday
Mr Clarke's speech is a brief summary of eight to 10 volumes of written material collated after more than four years of evidence-gathering.
It is intended to constitute an overview of the issues for the tribunal to decide and an indication of a range of conclusions the tribunal might reach.
The Bloody Sunday inquiry was established in 1998 by Prime Minister Tony Blair after a campaign by families of those killed and injured.
The inquiry has so far cost £130m and the final bill will be around £150m.
Hundreds of witnesses
BBC Ireland correspondent Mark Simpson said the Bloody Sunday inquiry has been "the longest inquiry in UK legal history".
He said the final report and its conclusions will not be made public until the summer of next year.
More than 900 witnesses have given evidence to the tribunal since Lord Saville of Newdigate and the Commonwealth judges accompanying him on the inquiry began their work in March 2000.
Only when Mr Clarke has finished the closing speech stage of the tribunal will the three inquiry judges sit down to write their report.
The inquiry has heard evidence from leading politicians, including the prime minister at the time, Sir Edward Heath, civilians, policemen, soldiers and IRA members.
The leader of the Official IRA on Bloody Sunday had been due to give evidence on Friday but pulled out through illness.