Today's evidence may focus on foreign exchange transactions, an issue central to the controversy about the Taoiseach's finances, writes Colm Keena.
Today could be a crucial day in the ongoing saga of the finances of Taoiseach Bertie Ahern.
The likelihood is that the Mahon tribunal will begin hearing evidence directly concerned with Mr Ahern's finances, although the tribunal's intended sittings on the matter could still be cancelled as a result of a court challenge by Mr Ahern.
Today's evidence, if heard, will be focused on matters to do with foreign exchange transactions, an issue that has become central to the controversy concerning four large lodgments made in 1994 and 1995 by Mr Ahern and his then partner Celia Larkin.
On December 5th, 1994, Ms Larkin lodged £28,772.90 to an account opened in her name in AIB O'Connell Street, Dublin.
She has told the tribunal the lodgment occurred after a Manchester-based businessman, Michael Wall, gave Mr Ahern £30,000 sterling in cash for expenditure on a house Mr Ahern was to rent.
The tribunal has found that the lodgment equates to $45,000 at one of the exchange rates operated by the bank on that date, though not the rate that should have been applied given the amount lodged.
The tribunal has also discovered that total sterling transactions at the bank branch on that day amounted to a value of only £1,921.55.
In other words, the details of how the lodgment came about, as outlined by Mr Ahern and Ms Larkin, conflict with the bank's records. Mr Ahern, for his part, has said he has never been involved in any dollar transactions. The whole controversy over Mr Ahern and his finances in the early 1990s has come to zero in on this lodgment.
When the tribunal read out an opening statement on the issue in May, it had not discovered any documents in the bank's files that could show definitively what currency was lodged. Whether that situation has change is not known.
John Garrett of AIB is scheduled to give evidence this afternoon as an expert witness on foreign exchange transactions. The key issue he will deal with, directly or indirectly, is whether Mr Ahern's version of events can be correct, given the facts that are known.
On Thursday, Philip Murphy, the official at AIB O'Connell Street who dealt directly with Mr Ahern during the early 1990s, is scheduled to give evidence.
Jim McNamara, another official who worked at the O'Connell Street branch in the 1990s, will give evidence on Friday.
On Tuesday, another official from the branch, Elaine Blake, will give evidence, as will Rosemary Murtagh, who will give expert evidence on currency matters. The original list of witnesses the tribunal intended to call from AIB, did not include Ms Murtagh.
Mr Wall and Ms Larkin are scheduled to give evidence on Wednesday, to be following on Thursday, and possible also Friday, by the Taoiseach.
This month, in an interview with the Sunday Independent, Mr Ahern said he was looking forward to going into the tribunal and vindicating his good name. During the general election campaign he said he could answer the questions that have arisen.
However, on Friday his lawyers sought to prevent the matter being dealt with in public evidence and, following the tribunal's rebuttal of that submission yesterday, Mr Ahern's remaining option is to decide to send his legal representatives into the High Court to continue with their effort to prevent the scheduled hearings going ahead.
To do this his legal team would seek a judicial review of Judge Mahon's ruling. If an application for a judicial review was granted, Mr Ahern's lawyers would seek to have the hearing of evidence suspended until the matter can be heard.
Such a scenario could see the hearing of evidence on Mr Ahern's finances put back until next year and, if his lawyers were successful, evidence concerning Mr Ahern's personal finances never being heard.