Mr Charles Haughey's former special adviser said she tore into "little pieces" her personal diary containing the utmost personal, political secrets of the former Taoiseach a week or two after a meeting with Ms Eileen Foy, his former private secretary.
Ms Catherine Butler said the tribunal had not contacted her when the diary was destroyed in the summer of 1998, but it had contacted Ms Foy.
Ms Butler told the tribunal: "My personal journal contained details of my family life, my personal life, the utmost personal, political secrets of Charles Haughey, such as the formation of the coalition government of 1989, where only I and Mr Haughey would have been in possession of certain information."
She tore it and put it in the bin after the meeting with Ms Foy at Ballymore Inn in Co Kildare. At the meeting, Ms Foy asked for help with information after the tribunal had asked her questions, particularly in relation to the party leader's allowance account.
Mr Jerry Healy SC, for the tribunal, asked that in destroying the document did she not know she was destroying material relevant to the tribunal's terms of reference. Ms Butler repeated the tribunal had not contacted her at that stage.
Mr Adrian Hardiman SC, for Ms Butler, said his client had co-operated with the tribunal and now there seemed to be a suggestion of impropriety.
Ms Butler asked if she was being accused of wrong-doing in destroying her personal diary or of any criminal activity. The chairman said there was no question of any wrong-doing or being accused of anything.
She said Ms Foy wanted to use the diary to confirm certain matters, but Ms Butler said she wanted Ms Foy's memory to be her own. When Mr Healy put it to her that all Ms Foy was trying to do was confirm dates, Ms Butler said, "I think she wanted to do more." She said at that stage she did not want to be drawn into the tribunal. She later said she felt "rotten" for not being able to help Ms Foy.
"What prompted the meeting was Ms Foy's distress as she found it at being unable to respond to certain queries, in particular to pinpoint certain events, to put them in context or to date them," said Mr Healy.
Ms Butler agreed and said: "She was extremely distressed following a meeting with your good selves, and she produced a typed list from her handbag with figures and dates, which she said the tribunal have identified for me, they had identified amounts over the sum of £5,000 for which they sought an explanation.
"She pointed to the middle of the list, and for a very large sum of money and the date was 1987, and she said this related to Brian's transplant costs, Catherine.
"And I told her no, it didn't, because Brian didn't go to the Mayo clinic until May of 1989. And she broke down and cried. And said she had told the tribunal that this is what this particular large amount related to and she did not know how she could recall these details. And she was just so distressed," said Ms Butler.
Ms Butler also revealed that Mr Bertie Ahern on one occasion between 1987 and 1990 signed a full book of blank cheques.
However, she said up to 1987 it was a "rare occasion" for Mr Ahern to pre-sign cheques in this way. She said he normally signed cheques which had the details filled in. However, after 1987, when Mr Ahern became minister for labour, he was very busy and hard to pinpoint, she said. She said Mr Ahern was known as "the Scarlet Pimpernel" because he was so hard to get a hold of. She said before 1987 she often saw cheques waiting to be signed by Mr Ahern with invoices attached to them.
Earlier, Ms Foy told the tribunal she did not think she ever asked anybody to sign a full cheque book.
"I do not remember Mr Ahern ever signing a full cheque book," she said. Asked if it could have been up to 20 cheques, Ms Foy said they could see from the statements the amount of transactions each month so it could have been 20.
Tribunal counsel asked who initiated the practice of having cheques pre-signed. Ms Foy said she did not know.