The chairman of the Bloody Sunday inquiry made a last-ditch appeal yesterday for anyone who can help the tribunal to come forward and give evidence.
Lord Saville made the fresh appeal as he signalled that oral evidence to the inquiry will be completed by Christmas.
Speaking ahead of Thursday's summer recess, he said the inquiry would hear all the evidence of military witnesses in London.
It would then return to Derry in the autumn to hear the evidence of Mr Martin McGuinness MP, of Sinn Féin, and a number of members of the Official IRA at the time.
He warned that anyone who could help the inquiry but who had not done so was doing a "great disservice" to the search for the truth of what happened on January 30th, 1972.
"The process of seeking and taking evidence cannot, obviously, continue indefinitely," he said.
"I want, therefore, to urge those with whom the inquiry had been in contact, or who know that the inquiry has been trying to contact them, but who have not so far assisted the tribunal, to provide all the assistance that they can in the provision of information and, where relevant, evidence, and to do so as soon as possible."
Lord Saville said there were a number of areas in which evidence that ought to be provided was still absent.
"If significant evidence that could be given is not given, that will have two consequences," he said.
"Firstly, it will be a grave disservice to the search for the truth of Bloody Sunday, and, particularly, the relatives, who have so long sought it.
"Secondly, at the end of the day we shall have to reach a judgment on all the evidence that we have heard.
"But, in reaching that judgment, we may also have to take into account the fact, if it turns out to be one, that people who could have given evidence have chosen not to, since that fact may have a significance of its own.
"In the relatively few cases where a traced individual has remained unresponsive, the tribunal will decide whether or not to use its powers of subpoena," he said.
"The inquiry is also in contact with a number of witnesses or potential witnesses from whom it may wish to take a statement and those discussions will continue."
The inquiry will resume at Methodist Central Hall in London on Monday, September 8th, and run for about six weeks, before returning to Derry after a short break, he confirmed.
"When we return to the Guildhall we shall be hearing the witnesses who could not be heard during previous sessions there, as well as those who have come forward since then, the Official IRA witnesses, Mr McGuinness and various others who we believe may be able to help us," Lord Saville said.
"If necessary we shall continue sitting until Friday, December 19th."
Later yesterday a soldier was accused of suffering from "wilful blindness" when he claimed that he did not see a number of people killed in Derry on Bloody Sunday.
Mr Arthur Harvey QC, representing most of the families of the dead and wounded, put it to Soldier 017 that he must have seen more than he claimed to on January 30th, 1972, when 13 civil rights marchers were shot dead by soldiers.
A 14th man died later.
The former private in Mortar Platoon of the Parachute Regiment said he only saw one man shot near a rubble barrier on Rossville Street, at which five people were killed.
Mr Harvey said: "I suggest to you what you suffer from is wilful blindness.
"You have made a determined effort to see nothing in relation to the deaths you must have witnessed of at least five people at that barricade and the movements of Anti-Tank Platoon into Glenfada Park where they carried out four further murders and you claim to have really seen nothing of what went on?"
"Correct," replied the soldier.
Soldier 017 said he saw Soldier P shoot a nail-bomber near the rubble barricade, despite the fact that Soldier P said he shot the man in a different location, as he emerged from an alley.