The Banking Inquiry is due to hear from one of Brian Lenihan's closest civil servants at the time of the bank guarantee.
Kevin Cardiff was in charge of the Department of Finance's banking unit at the time.
He was one of the people in the room on the night the bank guarantee was issued. He has claimed that foreign governments started to spread rumours of Ireland going into a bailout, long before a decision was made.
The Banking Inquiry has asked the Gardaí to investigate how so much of Mr Cardiff's evidence was published by the Sunday Business Post, four days before his appearance.
Mr Cardiff's 380-page written statement will today be added to by hours of testimony before TDs and Senators who will want to know more.
Kevin Cardiff is now Ireland's member of the EU Court of Auditors. Before that he was Secretary General at the Department of Finance - its top civil servant.
Before that he was the second-in-command who led the Department's banking unit - meaning he was the main contact point with bank regulators and the banks themselves.