The chairman of the Disclosures Tribunal has described as "bizarre" and "really strange" that former garda commissioner Martin Callinan would draft a response for a solicitor facing a threat of legal action from Sergeant Maurice McCabe.

The Disclosures Tribunal is examining an alleged senior garda smear campaign against Sgt McCabe.

The inquiry has heard that solicitor Gerald Kean appeared on RTÉ's Marian Finucane show on 26 January 2014.

He spoke by phone to Mr Callinan several times before the show discussing the penalty points issue and whistleblowers.

During the programme, Mr Kean said that whistleblowers had not co-operated with an internal garda inquiry on the quashing of penalty points.

He told the tribunal that the incorrect information had come from Mr Callinan.

Sgt McCabe began a legal action against RTÉ and Mr Kean, who forwarded the letter to Mr Callinan seeking his assistance in responding.

Today, Mr Callinan's former private secretary, Superintendent Frank Walsh, gave evidence that Mr Callinan wrote out four paragraphs in response to Mr Kean's request.

Supt Walsh met Mr Kean on 12 February 2014 and passed on the information.

The tribunal heard these four paragraphs largely made their way into Mr Kean's response to Sgt McCabe, although Mr Kean's letter made no reference to the commissioner's input.

Mr Justice Peter Charleton said it was not part of the commissioner's duties to respond to the complaint as it involved two private citizens having a row.

He said he could not think of anything stranger than for a commissioner to respond in this way to a "well-known solicitor".

He said it was "really, really, really strange" and "bizarre".

Supt Walsh said it was most unusual and inappropriate. He also said that he was not aware that Mr Callinan had spoken to Mr Kean before the programme.

Counsel for the tribunal asked Mr Kean whether he thought the commissioner was deceiving him, he said he certainly did not have all the information. He said he would have dealt with it differently if he knew then what he knows now.

Mr Justice Charleton suggested to Supt Walsh that he must have thought Mr Callinan had lost all touch with reality.

He also said Mr Kean, Mr Callinan and Supt Walsh did not tell the tribunal about the correspondence and it was rooted out by the tribunal's investigators.

Supt Walsh said they were not trying to hide the interaction.

Lawyer for Supt Dave Taylor, Michael O'Higgins, said the interaction was unattributable and untraceable to Mr Callinan as his name was not mentioned in Mr Kean's response to Sgt McCabe.

The tribunal has concluded its hearings on this section of the inquiry and will resume sittings on Monday 30 April.