The film and still photographs showing a young Father Daly, waving a bloodstained handkerchief, leading a group of men carrying the body of a teenager from the Bogside, have come to symbolise the events of January 30th, 1972.
Much of Dr Daly's evidence will relate to the death of 17year-old Jackie Duddy, who was the first of 13 people killed in Derry on that day. He will also be cross-examined yet again on the evidence he gave at the 1972 Widgery Inquiry that he saw a man fire a pistol in the car park of the Rossville flats shortly after Mr Duddy was shot dead by a paratrooper.
This civilian gunman, whose shadowy outline can be seen in some press photographs of the day, has been the subject of much speculation in the years following Bloody Sunday, and has become known as "Father Daly's gunman". Dr Daly will join a series of inquiry witnesses who have described seeing civilian gunmen at various stages of the events on the day.
Last week a former BBC radio reporter, Mr David Capper, described hearing a shot fired, ap parently towards soldiers in a derelict building, by a civilian in the William Street area 20 minutes before the paratroopers entered the Bogside.
He saw a man in a brown overcoat place a handgun in his pocket and run away. Another witness, Mr Ciaran Donnelly, who was a staff photographer for The Irish Times, also described seeing a man in his 40s, who appeared to be drunk, firing a shot from a small handgun "or possibly a starting pistol" in the same area.
A number of other witnesses have given, or will give evidence of seeing a civilian gunman in the same general area at about the same time. An important aspect of the inquiry's task will be to analyse these various accounts and try to ascertain how many of them relate to the same incident and the same gunman. There is also speculation whether the gunman was the same person seen some time later in the Rossville Flats car park.
Counsel for the soldiers who were involved in the shootings have sought to emphasise the role and impact of these civilian gunmen on the events of the day and have suggested that a number of people were hit by army gunfire because they were in close proximity to such gunmen.
The 1972 report of Lord Widgery said that civilian, as well as army, evidence "made it clear that there was a substantial number of civilians in the area who were armed with firearms".
Lord Widgery commented: "I would not be surprised if in the relevant half hour, as many rounds were fired at the troops as were fired by them. The soldiers escaped injury by reason of their superior field-craft and training." He was "entirely satisfied" that the first firing in the car park of Rossville Flats was directed at the soldiers.
The Widgery report, which broadly exonerated the soldiers and stated there was no general breakdown in discipline, was criticised and discredited in a number of respects. It lasted just three weeks and heard fewer than 60 civilian and press witnesses.
Fresh evidence and a long campaign by relatives of the victims led to the establishment in 1998 of the present inquiry, which has so far heard direct evidence from 70 civilian witnesses out of an expected total of more than 500.
Intense media interest is expected to focus on Dr Daly's attendance at the inquiry today. He will relate once again how he gave the Last Rites to Mr Duddy as he lay dying in the car park, and how he afterwards led the group which carried the body to an ambulance.
Dr Daly retired in 1993.