Bertie Ahern said Ms Carruth had been harangued by the tribunal.
He said she was not withholding any information from it, but simply could not remember the answer to questions she was being asked.
Mr Ahern also clarified Dáil comments he made yesterday. The Tasoieach said he was referring to the Mahon Tribunal when he said that not all chambers were as fair to him as the Dáil.
Meanwhile, a former AIB manager has told the Mahon Tribunal that the bank was not informed of payments to Frank Dunlop for the Quarryvale development.
Eddie Kay, a former manager at the bank's corporate division, said the bank was not asked for approval of payments to Mr Dunlop's company Shefran and was not provided with invoices.
Mr Kay said he was not made aware of Shefran payments in 1991, totalling £80,000, until the following year.
He said he did not notice the lack of VAT element on the round figure sums.
He deduced they were fee payments as distinct from reimbursement of outlay expenses made to the company Frank Dunlop and Associates.
Mr Kay said he did not consider the figures to be out of line considering the scale of the Quarryvale development.
The Tribunal heard the payments were made by developer Owen O'Callaghan then jointly involved with Tom Gilmartin in getting rezoning for the west Dublin site.
Under questioning by Tribunal counsel Mr Kay said Mr Gilmartin had told him that he did not like Mr Dunlop but did not say why.
He said Mr Gilmartin did not say that he considered Mr Dunlop to be a bagman for politicians.
