Whistleblower Frank Dunlop altered his diaries to remove references to Taoiseach Bertie Ahern and his FF predecessor, Albert Reynolds, it has emerged.
He also scrubbed out entries relating to former Environment Minister Padraig Flynn and to former Sports Minister Liam Aylward.
The former lobbyist, who promised to spill the beans on corruption in the planning process in Dublin by naming those he said he bribed to get land rezoned, said he couldn't give any reason for his decision to alter his diaries.
He did not deliberately conceal the information, he omitted it, he told the planning probe.
But, tribunal judge Gerald Keys rounded on the lobbyist, saying that his answers to these crucial questions didn't make sense and went to the heart of his credibility in a large way.
"I find it very difficult to accept your answers, they don't make sense," Judge Keys added.
The diaries, which Mr Dunlop relies on as part of the "roadmap" of planning decisions, and politicians and business people he met in his career as a lobbyist for developers, were changed after Mr Dunlop had undertaken to fully co-operate with the planning probe.
Mr Dunlop said he couldn't explain why he had taken out references to senior politicians or to "the big one", which he now says relates to a IR£500,000 success fee he was to get from developer Owen O'Callaghan for lifting the cap on the size of Quarryvale.
Yesterday, he told the tribunal he had no idea when he wiped out at least four references to the "big one" after he had agreed to fully co-operate with the planning probe.
He agreed with tribunal counsel Patricia Dillon SC that his decision to remove the references to Mr O'Callaghan and "the big one" was one which he made consciously.
On December 10, 1993, Quarryvale was successfully confirmed by the Co Council and three days later Mr Dunlop wrote in his diary, "discussion re Big One, when if deal comes through, 'private' deal when, leave to FD".
This entry, however, did not appear in the redacted diary which he provided to the tribunal, but he couldn't say now why he wanted to keep this information from the tribunal.
"You excluded it because you did not want the tribunal to know about it," said tribunal chairman, Judge Alan Mahon.
In relation to the senior politicians, Mr Dunlop said that he did not make a decision to exclude the reference to the senior politicians from the edited diaries he provided to the tribunal.
"I never in my life spoke to Bertie Ahern in relation to Quarryvale, except to ask him, as Taoiseach, to perform the official opening of Quarryvale," he added.
Mr Dunlop said he hadn't spoken to either Mr Flynn or Mr Reynolds about Quarryvale, although he had spoken to two of the politicians about the proposed National Stadium.
Asked if the reference to "the big one" could be to do with the Stadium, rather than a success fee for the lifting of the cap on Quarryvale, Mr Dunlop said he was loathe to say this was the case.
He did have discussions with Mr O'Callaghan, architect Ambrose Kelly and Liam Lawlor about the stadium.
He said that he couldn't explain either why he had removed several references from his diaries to the late Liam Lawlor.
He had always told the tribunal that Mr Lawlor was heavily involved with Quarryvale.