The financial services regulator is now switching its attention to whether there was a cover-up about the charging of incorrect foreign exchange fees at AIB.
This follows an interim report, published yesterday, which found it had overcharged customers in a range of areas by over €34 million.
The chief executive of the Irish Financial Services Regulatory Authority (IFSRA), Mr Liam O'Reilly, said it was "strange" the bank could have charged an incorrect fee on foreign exchange transactions for eight years without this issue coming to light.
He was speaking at the publication of an interim report concerning charges imposed by AIB since September 1995. The bank is to repay €34.2 million in charges and interest to customers. As well as the foreign exchange overcharging which had already come to light, the inquiry uncovered 24 other areas where 70,000 customers had been overcharged to the tune of €8.1 million. The bank is promising to repay all this money with interest.
Asked if he believed there had been a cover-up at the bank about the foreign exchange issue, Mr O'Reilly said IFSRA wouldn't be having an investigation into AIB "unless we had grounds to believe there was some sort of cover-up".
He said the investigation was "well advanced" but people had constitutional rights and everyone had to be given a right of reply.
At a separate press conference the chairman of AIB, Mr Dermot Gleeson SC, said the bank didn't get its charges notification right for eight years and "you'd have to ask questions".
A second report due in the autumn will, among other matters, focus on how AIB could have charged an unauthorised rate for foreign exchange transactions for eight years without the matter being brought to the attention of the regulator.
It will seek to establish who, if anyone, was "culpable".
The bulk of the money to be returned by AIB (€25.6 million, including interest) arises from foreign exchange transactions where the bank charged margins that were double those notified to the regulator.
The margin charged was the one advertised to the public and a competitive rate. The bank is not obliged to return the money but will do so.
Investigations by IFSRA and AIB have also uncovered instances where customers of the bank were charged more than the advertised rate for 24 products or services. The bank is obliged to return the €8.1 million involved in those instances, and is to do so.
Among those affected are 4,200 AIB mortgage customers, who were not given discounts that they should have received, involving a total of €3.6 million.
Mr Gleeson told the press conference he wished to say how sorry he was, and the bank was, "for the regrettable lapses and errors that have occurred, and how determined I am, and we are, to put things right".
He said the charging by the bank of more than the notified fee was a serious matter but that, in his view, a perhaps more serious matter was the breach of the trust that should exist between the bank, its customers, and its regulator.
The AIB Group chief executive, Mr Michael Buckley, said that while the bank failed to notify the regulator in relation to the charges imposed, it had not overcharged foreign exchange customers.
Mr Gleeson said that when a bank "messes up like this" it was appropriate that "contrition is demonstrated".
Asked about careers coming to an end at the bank, Mr Gleeson said he liked to think the bank would deal humanely with people who made mistakes in the course of their work, but it would be less forgiving with people involved in "disguise or covering up".
Mr Buckley said that when the issue with foreign exchange charges was brought to his attention, the bank went through a process where it "tore up the floorboards" and during which other charging issues emerged.
The bank has announced a number of initiatives, including a confidential helpline based in Britain, to assist "whistle-blowing".