A Garda whistleblower told a detective superintendent he was going to "take down" former garda commissioner Nóirín O'Sullivan and wage "all out attack" on management, a tribunal has heard.

Garda Nicholas Keogh was giving evidence at the Disclosures Tribunal where counsel for An Garda Síochána are cross-examining him.

The tribunal is in its second week hearing from Gda Keogh who alleges that a senior member of the Athlone drugs unit, identified to the tribunal as Garda A, was in an improper relationship with a heroin dealer, identified as Ms B, who had a then-estimated €2,500 a week income.

The tribunal, chaired by Judge Sean Ryan, is investigating how Gda Keogh was treated after he made his protected disclosure in 2014.

Counsel for the gardaí, Shane Murphy SC, went through Gda Keogh's diary entries.

In December 2014 and May 2015, Gda Keogh met then TDs Clare Daly and Mick Wallace about his case.

At the first meeting, Gda Keogh wrote that the smell of the wine they were drinking was "unnatural", described himself as "like a bloodhound" but told Judge Ryan that he was "in a bad way" at the time with his drinking.

At another meeting, Clare Daly told Gda Keogh: "Don't worry, we will get them in the end."

Gda Keogh told Judge Ryan that the "them" referred to was "Garda management" but that Deputy Daly was "only offering encouragement" to him.

Mr Murphy then asked if Gda Keogh was out to "get" people and was told "no".

"In May, 2015, the gardaí have already embarked on a cover up and I'm under pressure from Garda management," said Gda Keogh. "It's a parallel thing."

Garda Nicholas Keogh

An entry on 1 January, 2018, reads: "Fourth years of this s***." On 22 January, 2018, he wrote: "Nóirín in tribunal said she supported all whistleblowers."

As part of the investigation into Gda Keogh's original collusion complaint, Detective Superintendent Declan Mulcahy met and regularly updated Gda Keogh.

Det Supt Mulcahy also kept in contact with Gda Keogh's superior Superintendent Noreen McBrien about welfare issues regarding Gda Keogh's drinking and health.

In April, 2015, Det Supt Mulcahy said that there was concern for Gda Keogh and that welfare services were there for him.

The tribunal heard that Gda Keogh texted while drinking: "I will accept welfare if you are still offering".

In September, 2015, he met a welfare officer, Mick Quinn, who Gda Keogh said was "brilliant, brilliant throughout the last couple of years".

Det Supt Mulcahy wrote that before meeting the welfare officer that conversations with Gda Keogh were sometimes when he was drunk.

"He did not make a lot of sense and spoke of 'bugs' and talked about a gun in someone's mouth," wrote Det Supt Mulcahy in October 2014 and that in November 2014 Gda Keogh said: "make up your f***ing mind, you are pussy-footing around".

Det Supt Mulcahy wrote after two incidents that he would talk to Gda Keogh again when he was sober.

In April, 2015, Det Supt Mulcahy wrote that Gda Keogh spoke of "all-out attack and of taking Nóirín O'Sullivan down.

He asked if Gda A was going to be arrested and also mentions Alan Shatter and that he was also going to take him down."

Mr Murphy asked if that in April 2015 was Gda Keogh's attitude to "take down" people from office.

"I had a firm view on Nóirín O'Sullivan," said Gda Keogh, adding that he did not want to take down everyone just a "cabal" and that he had no issue with Alan Shatter.

Judge Ryan asked "Did that represent your state of mind, or was it a drunken state of mind?"

"A bit of both, to be honest," Gda Keogh told the judge.

Det Supt Mulcahy also noted that Gda Keogh, when contacted, told him that he was at home "playing around with his computer putting pictures of rats on Nóirín O'Sullivan".

"He mentions that Aidan Glacken was going to be promoted and that he couldn't allow that. It was a circus of madness and that he was going to make a film about it."

Gda Keogh said that he "wouldn't have that level of knowledge on a computer to do that. Email was still a new thing to me. I still work off old phones. I wouldn't have the knowledge in relation to that particular thing."

Mr Murphy asked if Gda Keogh told Clare Daly, Mick Wallace or whistleblower Sergeant Maurice McCabe that he "had ideas about taking down Nóirín O'Sullivan."

Gda Keogh said: "No, no, no".