O'Sullivan's lawyers also represented officer 'extremely hostile' to McCabe
Former Garda commissioner Nóirín O'Sullivan has denied a conflict of interest arose when her legal team at the O'Higgins Commission also represented a senior officer who believed Maurice McCabe was out to destroy his career.
Michael McDowell SC, for Sgt McCabe, told the Disclosures Tribunal "bad blood" had existed and Supt Noel Cunningham was someone who "had an extremely hostile attitude to Sgt McCabe".
He said Ms O'Sullivan's position was that she wanted an impartial investigation of issues at the commission, yet she was using the same counsel as an officer who believed Sgt McCabe was out to ruin him.
This, he said, was a "manifest conflict of interest" - a significant issue.
While Ms O'Sullivan instructed her lawyers to test Sgt McCabe's allegations by challenging his credibility and motivation for making complaints, counsel Colm Smyth SC went further and questioned the whistleblower's integrity.
As well as Ms O'Sullivan, Mr Smyth represented five other senior gardaí, including Supt Cunningham and others, against whom Sgt McCabe made serious complaints.
The allegations against Supt Cunningham were ultimately dismissed or found to be unjustified.
During her third day giving evidence at the tribunal, Ms O'Sullivan said she did not know what Supt Cunningham had said in private consultations with the Garda legal team and did not discuss his evidence with him. She insisted she was never informed of any potential conflict of interest.
If one had arisen she would have been advised of the need for the officer involved to get separate representation.
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Supt Cunningham was the officer who investigated an allegation that Sgt McCabe had sexually assaulted the daughter of a colleague. The DPP decided no crime had been committed.
The tribunal has previously heard he believed there was a change in Mr McCabe's attitude after the sergeant was unable to get the full DPP directions in the case, as this would have been contrary to procedure.
It heard yesterday how Supt Cunningham told the O'Higgins Commission he believed Sgt McCabe had undermined him "at every turn".
Later, Ms O'Sullivan said she was at a loss to understand why Sgt McCabe had decided he could no longer continue as sergeant in charge of the traffic unit in Mullingar.
The tribunal had previously heard Sgt McCabe told his superintendent he felt "under threat" from Ms O'Sullivan and that if anything went wrong "they would be down on him like a tonne of bricks".
Sgt McCabe made the remarks on May 18, 2015, just three days after the commission was told by Mr Smyth that he had been instructed to challenge the whistleblower's integrity. But Ms O'Sullivan said she "couldn't make the connection" between what was going on at the commission and Sgt McCabe's feelings of being under threat.
Mr McDowell took issue with this and asked if she had not sought to find out if something had occurred at the commission to make Sgt McCabe react in the way he did.
Ms O'Sullivan said her liaison officer Chief Supt Fergus Healy had briefed her, but she wasn't aware of the specific words used by Mr Smyth. She said that once her legal instructions had been given, the questions and the words used were up to the lawyers and not her as a client.
"That is the latitude that the lawyers had," she said.
Mr Smyth clarified on November 4, 2015, after being asked about it by Mr Justice Kevin O'Higgins, that he made an error when he said he was challenging Sgt McCabe's integrity.
The barrister will be giving evidence when the tribunal resumes today.
In its current module, the tribunal is investigating whether Ms O'Sullivan relied on unjustified grounds to discredit Sgt McCabe at the commission, which investigated allegations of malpractice in the Cavan/Monaghan Garda division.