The Taoiseach has been asked to explain to the Mahon tribunal why he did not disclose the fact that an account opened with £50,000 in December 1994 in his former partner Celia Larkin's name was to be used for his benefit.
Mr Ahern had earlier agreed in testimony that the account, although opened in Ms Larkin's name, was used for his benefit. "It was my money," he said.
The account at AIB O'Connell Street, Dublin, was opened on December 5th 1994 on the same day Ms Larkin lodged the money handed over to Mr Ahern by businessman Michael Wall.
It was composed of a sum of £28,000 and a sum of £22,000 transferred from Mr Ahern's own accounts, but it was Ms Larkin who signed the documentation to open the account at the bank.
Mr Ahern was in Brussels and said he had authorised the bank to open the account and to transfer the funds.
Counsel for the tribunal Des O'Neill asked Mr Ahern why he did not give details of this account in the discovery process and why he had not believed the account fell within the terms of the information the tribunal had asked him to produce.
Conor Maguire SC for Mr Ahern objected to the line of questioning and said Mr Ahern was not being accused of non-co-operation with the tribunal's order for discovery.
However, tribunal chairman Alan Mahon intervened and said Mr O'Neill was entitled to ask about information which was not previously known.
Mr Mahon asked Mr Ahern could he explain why, given the information now known about the £50,000 in Ms Larkin's account, this was not included in his own affidavit of discovery - ie the documents he was obliged to give the tribunal.
Mr Mahon asked the Taoiseach why his solicitor had "merely indicated" in his letter to the tribunal that a transfer of money had taken place to Ms Larkin "without saying it was to be for your benefit".
Mr Ahern said Ms Larkin was his partner at that stage, and he assumed that by giving the tribunal the reference to the account and the account numbers, he was making the tribunal aware of the information.
In an exchange with Mr O'Neill shortly before the tribunal took a break at 11.45, Mr Ahern said he still did not understand why the tribunal was investigating his house at Beresford Avenue.
The Taoiseach said he did not understand what this had to do with allegations that he took payments from Owen O'Callaghan, did not understand what Celia Larkin had to do with the allegations about Mr O'Callaghan and did not understand what Michael Wall had to do with it.
The £28,000 transferred into that particular account came from his own special savings account and the £22,000 was money given to him by friends; it went through his accounts and was his money, Mr Ahern said.
The Taoiseach was also asked to explain why he did not give the tribunal back-up documentation in relation to lodgements to his accounts until March 2006 when it had been in his possession since January 2005, just before he swore his first affidavit of discovery.
The documentation includes a file note from bank official Jim McNamara of AIB, which was only seen by the tribunal after it made an order of discovery against the bank to disclose its own files, counsel for the tribunal Mr O'Neill said.
That note outlined details of certain transactions in response to Mr Ahern's own inquiries of AIB in relation to a number of large transactions on his accounts.
Mr Ahern said that to his recollection, any documentation he had was sent to the tribunal with the first order for discovery.
Mr O'Neill said Mr Ahern could take it "as fact" that the information was not given to the tribunal until March 27th 2006. The documentation was received by Mr Ahern's secretary in January of 2005, the tribunal heard.
Mr Maguire, for the Taoiseach, argued that in November 2004, the tribunal had said Mr Ahern could limit the production of documents to items over £30,000.
However, Mr O'Neill for the tribunal argued that there was a difference in legal terms between "production" and "discovery" and that Mr Ahern had been obliged to discover that back-up information in relation to his accounts.