The Sinn Fein chairman, Mr Mitchel McLaughlin, yesterday strenuously denied any specific knowledge of the membership or organisation of the Provisional IRA in Derry at the time of Bloody Sunday.
Under persistent questioning by lawyers for the tribunal as well as legal representatives of British soldiers, Mr McLaughlin also maintained that he did not know, then or now, whether his Sinn Fein colleague, Mr Martin McGuinness, ever had been a member of the IRA.
He agreed that he had heard of the comments made at the inquiry that there had been a "wall of silence" about the activities of the IRA around 1972.
He told Mr Gerard Elias QC, counsel for soldiers: "It is my view that a wall of silence is a characteristic of the IRA. They guard their secrets very carefully and jealously."
Mr McLaughlin came under pressure from Mr Christopher Clarke QC, counsel to the tribunal, in regard to his knowledge of Mr McGuinness's status in the republican movement.
Mr Clarke put it to him that Mr McGuinness had been one of the "IRA delegation" who went to the house of a junior NIO Minister, Mr Paul Channon, in Chelsea in July 1972 to meet representatives of the British government.
The witness agreed that he was aware Mr McGuinness was part of that delegation.
Mr Clarke: "That was an IRA delegation, was it not?" Witness: "I do not know whether they described it as such, or even the British government did."
Counsel: "Could you answer my question: in 1972, did you really think that Mr McGuinness was visiting the British government otherwise than as a representative then of the IRA?"
Witness: "It is not a matter that I have any information on or opinion on."
Mr Clarke played a video clip of a 1972 press conference held in Derry on the occasion of an IRA ceasefire in which Mr McGuinness was described in terms such as "the commander of the Provisionals in Derry".
The witness said he had never discussed that with Mr McGuinness. Mr McGuinness had never discussed IRA membership with him.
Counsel put it to him: "You ask this tribunal to believe that you do not know to this day whether Mr McGuinness is or ever has been a member of the IRA?"
Witness: "I have already said, and I will repeat for your benefit: it was my practice throughout my political career not to invite myself or not to interest myself in issues that were outside my field of activity.
"I was involved in Sinn Fein and I simply did not want to know that information because it was dangerous information."
Counsel: "Can I have a clear answer to my question: you do not know to this day whether Mr McGuinness is, or ever has been, a member of the Provisional IRA; is that your evidence?"
Witness: "That is my evidence and I have made it clear I would not ask any individual if they were members of the IRA.
"Indeed, anyone who would confirm that to me, I would regard as being in some way suspect or unreliable."
Earlier Mr McLaughlin also denied that he had any knowledge of the identity of "active service IRA volunteers" in the Provisional IRA in Derry on Bloody Sunday.
He said: "I did not know to my certain knowledge of any individual who was a member of the IRA."
Mr McLaughlin was also questioned about a passage in a recent historical book on the civil rights movement and the troubles in Derry.
The witness said he objected to being handed material to read when he arrived at the inquiry yesterday morning, and he had refused to do so.
"I found it highly unusual," he said. "I just wonder if that would be normal procedure. I have been on notice from the tribunal for some months now and I certainly was not expecting to be handed documents as I came here to give evidence.
"I would have assumed they would have had the courtesy of giving advance notice of that."
He added that he had no difficulty with being asked questions about the document - "my problem was being ambushed".
The chairman, Lord Saville, assured him that there was no intention on behalf of the inquiry to "ambush" anything he wished to say.
The document had only been supplied to inquiry staff the previous night by counsel for one of the soldiers, and it had seemed the best thing to do was to proffer it to him as soon as possible.
Mr McLaughlin said that he was happy to accept this explanation.