He doesn’t recoil at the claims, but he did express himself shocked here and there that they were being made.

He doesn’t suggest that various parties are acting in some form of conspiracy against him, to portray him in a poor light. But he just doesn’t know why people are saying these things about him.

The claims, if accepted, would amount to the garda commissioner of the day spreading scurrilous lies, most seriously that Sgt McCabe was the focus of an ongoing investigation into child sexual abuse offences.

The alleged motive for spreading the lies is that Sgt McCabe was highlighting uncomfortable truths about abuse of the penalty points system in road safety.

Yesterday, Mr Callinan spent his second day in the witness box. He was brought through the encounters he had with two TDs and the Comptroller and Auditor General at a crucial Public Accounts Committee meeting on January 23, 2014.

In Leinster House, prior to the meeting, he encountered Fine Gael TD and PAC member John Deasy.

The TD claims Mr Callinan told him Sgt McCabe “was not to be believed or trusted with anything”.

Not so, says Mr Callinan. “They’re not words I used nor are they words I would use about any member,” he told the tribunal.

The commissioner then met Seamus McCarthy, the Comptroller and Auditor General, who had compiled the report on the penalty points system which the PAC was about to hear. Mr McCarthy is clear on what he believes Mr Callinan said to him.

The accountant says that the commissioner said to him that Sgt McCabe “was not to be trusted, that he had questions to answer, and that there were sexual offence allegations against him”. The statement, tribunal lawyer Patrick Marrinan put it to Mr Callinan, “leaves no room for error here”.

Mr Callinan’s defence is that there must be some mistake. He didn’t say those things. “I do think there is some misunderstanding,” he told Mr Marrinan.

After the heated PAC meeting, committee chairman John McGuinness approached Mr Callinan to thank him for coming.

According to the TD, Mr Callinan began telling a story of how former garda John Wilson — who had also brought complaints of malpractice in the penalty points system — acquired the nickname Jockey Wilson.

And then, according to Mr McGuinness, Mr Callinan said, “and the other fella fiddles with kids. That’s the type of fucking headbangers I’m dealing with”. The “other fella” was a reference to Sgt McCabe.

Another mistake or misunderstanding. Mr Callinan said he never said any such thing, nor would he.

That was the first of two encounters over two days in January 2014 at which Mr McGuinness says he was told about matters of this nature by Mr Callinan.

Mr Marrinan put the sum of the parts to the witness.

“Here again, we have John McGuinness who is suggesting that you made derogatory comments about Sergeant McCabe immediately after the PAC meeting in a context where, completely independently, John Deasy is saying he met you and you spoke poorly of Sergeant McCabe.

"Seamus McCarthy is saying you referred to allegations of sexual assault. Then immediately after the meeting there is this blackening of Sergeant McCabe’s name, isn’t that right?”

The former commissioner’s reply was clear, in keeping with the whole tenor of his evidence.

I never said Sergeant McCabe was not to be trusted. The text you read out to me (extracts from statements of the above witnesses) that is not the language I would engage with with anybody and certainly not the type of language I would engage in when speaking of colleagues or former colleagues to a committee chair.

Later, Michael McDowell, counsel for Sgt McCabe, pointed to a letter circulated to stations in Cavan-Monaghan in 2011 which he said “belittled” Sgt McCabe’s complaints and was designed to “humiliate” him.

The lawyer also went through a report compiled on Sgt McCabe’s whole career, which was produced in late 2013, ahead of the January 2014 PAC meeting. This went as far back as 1992 to a minor complaint from a member of the public which was dismissed.

Then Mr McDowell explored how in 2013 a detective superintendent went to the home of a Mr Bernard McCabe, an estranged uncle of Sgt McCabe, on the basis that he said his nephew had quashed drink-driving convictions. This allegation was shown to have no basis.

There were also various unfounded complaints from this source against Sgt McCabe concerning “goats, drug dealing” and issues around how many cattle the sergeant had in a field.

Sgt McCabe was not informed about any of these allegations.

“This is what was happening in 2013,” the lawyer put it to Mr Callinan. “Senior gardaí were expending valuable time on dud allegations against Sgt McCabe.” Mr Callinan said a matter was investigated, he didn’t see anything more to it.

There was also evidence yesterday that the uncle was visited again as late as December 2016, this time by an assistant commissioner. Again, it turned out there was no basis whatsoever for any complaints against the whistleblowing sergeant.

Mr McDowell suggested that the various inquiries into Sgt McCabe, compiled in the 2013 document, showed “there was an attitude of deep suspicion and willingness to search the record for anything that could assist in damaging Sgt McCabe.”

Mr Callinan replied: “If you are suggesting that I had anything to do with this document or it was designed to bring down Sgt McCabe, nothing, but nothing could be further from the truth.”

The whole tenor of Mr Callinan’s evidence is that he thought Sgt McCabe was doing a service for the force by bringing forward his complaints of malpractice.

His evidence continues.