Counsel for Sergeant Maurice McCabe has accused Nóirín O’Sullivan of "a dark lie" in relation to a claim that former garda commissioner Martin Callinan had retired due to allegations of corruption made against him by Sgt McCabe.

Ms O'Sullivan was asked at the Disclosures Tribunal about a submission she made to the O'Higgins Commission, which stated that some people were forced to leave their positions due to allegations of malpractice and corruption.

Asked who was being referred to, she said that Commissioner Callinan had retired at that point in time.

Michael McDowell said he would suggest to her that this was a dark lie.

He said Mr Callinan did not retire because of allegations made against him by Sgt McCabe.

Mr McDowell said the only allegation made about Mr Callinan by Sgt McCabe was that he had improperly advanced the career of a senior officer.

The O'Higgins Commission concluded the allegation of corruption against Mr Callinan was unfounded.

Ms O'Sullivan said she did not want to put words into Mr Callinan's mouth as to whether that had contributed or not to his retirement, but she said to have an allegation of corruption made against you was one of the gravest allegations that could be made against an officer.

She said in the public and political mind corruption is corruption.

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Disclosures Tribunal: As it happened Monday

O'Sullivan denies finding fault with legal team

Earlier, Ms O'Sullivan told the tribunal that she was not finding fault with her legal team at the O'Higgins Commission of Investigation.

Ms O'Sullivan repeated that she had never instructed her lawyers to question the integrity of Sgt McCabe at the commission.

The tribunal is examining whether Ms O'Sullivan inappropriately relied on unjustified grounds to discredit Sgt McCabe at those hearings.

The O'Higgins Commission was set up in 2015 to investigate matters relating to policing in the Cavan/Monaghan Division.

Mr McDowell put it to Ms O'Sullivan during questioning today that on the third day of the O'Higgins hearings in May 2015 her legal counsel had done two things she said she had expressly forbidden – challenged Sgt McCabe's integrity and suggested he was acting out of improper motives.

Ms O’Sullivan said she had never instructed that Sgt McCabe's integrity be challenged.

She said she could not account for what had happened at the Commission.

Ms O'Sullivan denied that she was finding fault with her legal team and said they had a momentous task in acquiring all of the knowledge they had to acquire in a short space of time.

The former Garda commissioner also rejected suggestions her assurances of supports being put in place for Sgt McCabe were insincere or hypocritical.

She said she would not have invested her and other senior officers' time in supporting Sgt McCabe if she was being hypocritical.

Ms O'Sullivan denied that she drafted responses for the then minister for justice to deliver to the Dáil to address the controversy that erupted after the O'Higgins report was published.

Ms O'Sullivan told the tribunal that she just sent on facts in three emails to the minister on the morning Frances Fitzgerald was due to address the Dáil on the matter.

Counsel for the Tribunal Kathleen Leader repeatedly put it to Ms O'Sullivan that she was drafting speeches for the minister.

Ms O'Sullivan said that was not the case, she was just presenting facts and she said she had to know whether the minister had confidence in her, otherwise she would have to consider her position.

In May 2016, there were reports that Ms O'Sullivan had challenged Sgt McCabe's motivation at the private O'Higgins hearings.

The tribunal was shown several emails between department officials and Ms O'Sullivan and other emails between Ms O'Sullivan and the minister discussing the issue.

Ms Leader asked whether there was a coordinated reposed between the two.

She said they were not just sharing information, they were writing speeches for each other, even though the commissioner was supposed to be accountable to the department.

Ms O'Sullivan denied that there was a coordinated stance. She said they just passed on suggestions, but she said her response to the controversy would be her own statement reflecting her own personal beliefs and feelings.

'Unprecedented politicisation' of role of commissioner - O'Sullivan

Ms O'Sullivan said she had never experienced such a media vortex as that which followed after the O'Higgins report was published.

She said there was unprecedented politicisation of her role as garda commissioner and it was covered on every single news bulletin on every single hour.

She said the leader of the opposition, Micheál Martin, was asking her to consider her position. She said it was very personalised and she felt she was being used as a political football and that continued until she retired last year.

The former commissioner was also asked about final submissions to the O’Higgins Commission.

Ms Leader said that at its mildest they suggested Sgt McCabe was not making his allegations for genuine reasons on policing standards.

Ms O'Sullivan said she accepted that they were genuinely held beliefs but sometimes she said they were unsupported by evidence and the allegations had to be tested.

Ms Leader said that nobody was suggesting the evidence should not be tested - what was at issue was whether it was appropriately tested.

Ms O'Sullivan will continue her evidence when the tribunal resumes tomorrow morning.

Earlier, Tribunal Chair Justice Peter Charleton asked Ms O'Sullivan if she had been accused of using a false allegation of sexual abuse against Sgt McCabe during the O'Higgins proceedings.

Ms O'Sullivan outlined that she was facing suggestions that she had in some way attempted to impugn Sgt McCabe's integrity by using the innuendo of an abuse allegation.

She said this was never put during the O'Higgins hearings, but that in the political mind this was the charge she was facing after the controversy emerged over the legal strategy at the commission. She said it was an implied charge.

Ms O'Sullivan also rejected suggestions she was asked to consider withdrawing an instruction to challenge the integrity of Sgt McCabe at the O'Higgins Commission.

Ms O'Sullivan told the tribunal she did not remember any suggestion of withdrawing because there was never an allegation of bad faith against Sgt McCabe.

She said she did not ever recall being asked to withdraw anything because she did not think there was anything to withdraw.

Ms O'Sullivan said the legal approach to Sgt McCabe at the commission was never about questioning his mala fides, or bad faith, but it was all about getting the context and reasons why the whistleblower had alleged corruption and malpractice by senior gardaí.

The former garda commissioner was shown notes of meetings she held with her legal team in October and November 2015 in advance of her appearance before the O'Higgins Commission.

At the first of those meetings on 20 October, she said as a preamble they had discussed why it remained necessary to challenge the motivation of Sgt McCabe at the commission.

Ms O'Sullivan told the tribunal it was her duty to balance the rights of everybody, including Sgt McCabe and the individuals against whom allegations were being made.

She said it was a balance she had to strike.

Ms O'Sullivan told the tribunal she was conscious of the public confidence issues in An Garda Síochána as a whole.

McDowell and O'Sullivan clash over letter by counsel for O'Higgins Commission

Sgt McCabe's lawyer and Ms O'Sullivan clashed on the contents of a letter drafted by counsel for the O'Higgins Commission and handed in on 18 May 2015.

The tribunal has heard that one paragraph of the letter effectively accused Sgt McCabe of saying that he had blackmailed a colleague in order to get what he wanted.

That was not the case and Sgt McCabe had never relayed that to two gardaí at a meeting in Mullingar in August 2008.

Ms O'Sullivan said the letter contained factual inaccuracies. Mr McDowell replied that they were not and they were instead gross falsehoods.

Ms O'Sullivan said it was her understanding that two words were mixed up "to" and "against" and that was how the error emerged.

She said it was a significant error and it was identified. She said nobody had ever suggested Sgt McCabe had made complaints against Supt Clancy.

Mr McDowell put it to her that submissions one month later repeated the accusation. He said the submissions said precisely the same thing and elaborated.

Ms O’Sullivan said she understood that now.

Earlier, Ms O'Sullivan said she was at a loss to understand why Sgt McCabe may have felt he was under threat from her when he resigned his position as sergeant in charge of the traffic unit in Mullingar in May 2015.

The tribunal was shown a copy of correspondence outlining that at a meeting on 18 May 2015, Sgt McCabe told a senior officer he could not carry on in the role, and when he was asked why he said the reason was Ms O'Sullivan, and he said he felt under threat.

Ms O'Sullivan has told the tribunal that she could not figure out how his decision to step down might be connected to the O'Higgins Commission.

The decision came after a dispute had arisen at the commission over the garda legal team's approach to the questioning of Sgt McCabe, who was a witness at the inquiry.

Ms O'Sullivan said she was available for a consultation with her solicitor the weekend after the issue first arose on 15 May, however she said she never had the impression that a consultation was urgently needed.

The Garda Liaison Officer Chief Supt Fergus Healy previously told the tribunal that he had conveyed a request from solicitor Annmarie Ryan for an immediate consultation with Ms O'Sullivan that day.

Ms O'Sullivan said she was not saying that anybody was wrong in the matter.

She said if the impression had been given to her that Ms Ryan wanted a consultation she would have made herself available.

Yesterday, Ms O'Sullivan told the tribunal that she had no reason to challenge or impugn Sergeant McCabe's integrity in any way, and did not sanction such an approach at the O'Higgins Commission.

Additional reporting by Sinead Morris