The inquiry heard yesterday that the car dealer, Denis Mahony, had no documentation about the payment, even though he had kept detailed records of financial transactions, including political donations, throughout his long business career.
Tribunal barrister, Patricia Dillon said the £10,000 payment, as well as a £2,000 "success fee" which Mr Mahony gave to the political lobbyist appeared to be designed to be kept "under-the-books".
Mr Mahony acknowledged that it was probably the only occasion he had agreed to pay someone money in cash form. He also accepted that it represented "an entirely traceless transaction."
The tribunal is investigating claims by Mr Dunlop that he paid bribes to four Fianna Fáil councillors GV Wright, Seán Gilbride, Cyril Gallagher and Jack Larkin to support the rezoning of lands owned by Mr Mahony and Noel Fox, in Baldoyle.
Mr Mahony said Mr Dunlop had sought the payment in cash and he had agreed to the request because he was "so thrilled to get him as I had land idle for 12 years".
Asked if he knew that Mr Dunlop was going to pay some of his money to councillors, Mr Mahony replied: "It never, ever crossed my mind."
The elderly businessman, who is a close personal friend of Charles Haughey, was also unable to explain how he had obtained a map of his land which he gave to Mr Dunlop in March 1993.
Mr Mahony said he was unaware that the current Fianna Fáil TD, GV Wright had acted on his behalf to make a submission to rezone the lands a few month earlier.
Asked if it was not unlikely that Mr Wright would have acted without telling him, Mr Mahony replied: "Well, I know nothing of it."
Meanwhile, fresh evidence also emerged which shows extensive contacts between Mr Dunlop and several councillors in the run-up to a vote to rezone the Mahony/Fox lands.
Tribunal lawyers revealed that Mr Dunlop had just last week handed over new documents relating to incoming phone calls received at his Dublin office between March and April 1993.
They show that the Mr Wright and Mr Gilbride together contacted Mr Dunlop on 27 occasions over a seven-week period.
Five calls from Mr Wright occurred in the week before March 25, 1993 one of two dates on which Mr Dunlop alleges he handed over £2,000 to the current Dublin North TD in the bar of Leinster House.
Similarly, the phone records show that Mr Wright also contacted Mr Dunlop's office on four occasions in the week before the second date suggested by the political lobbyist in April 1993.
Asked why he had not disclosed these records in response to a tribunal order dating from November 2002, Mr Dunlop explained that he only discovered the documents at his home in Dunboyne last week when he was clearing away old gardening clothes from his garage. "I didn't know I had these documents," he remarked.
Mr Dunlop said it was inconceivable that he would have deliberately withheld the documents from the tribunal as they supported his earlier evidence about having a huge level of contact with councillors.
Mr Wright's solicitor, Martin Kennedy said the discovery of Mr Dunlop's phone records represented a "fortuitous finding". Another barrister demanded that a Tribunal official conduct a search of Mr Dunlop's home.