Businessman David McKenna has said he was not the source of a leak to The Irish Timeslast September which first disclosed that the tribunal was investigating payments to Taoiseach Bertie Ahern.
Mr McKenna said he had received a letter from the tribunal which he had shown to his solicitor and no one else.
He said that as a result of the leak he had journalists calling to his home and office. One journalist had even approached his mother. "For anybody to think I was going to put my family through that in any shape or form I find totally unbelievable," he said.
Counsel for Mr McKenna, Hugh Mohan SC, said his client's solicitor, Bernard McEvoy, was willing to swear that he had not been responsible for the leak. Two people in his office might have seen the document but Mr McEvoy was satisfied they had not divulged the content of the letter or shown it to anyone else. He said it was Mr McKenna's view that the leak came from the tribunal.
Tribunal chairman Judge Alan Mahon said the leak was damaging to the tribunal and Mr McKenna, and "we absolutely deplore that that was done".
"We accept what Mr McKenna said on oath, that he wasn't responsible for the leak," he said.
There was no evidence as to where it came from. "There were probably 20, 30, 40 people between everyone concerned who may have had access at some stage to the letter, or a copy of the letter".
The matter "remains under inquiry. It remains a mystery at the present time", he added.