In dramatic evidence to the Disclosures Tribunal, the former head of the Public Accounts Committee outlined rumours circulating around Kildare St about Sgt McCabe in early 2014.
These were “malicious” and included suggestions Sgt McCabe was involved in sexual abuse and that he was a paedophile.
The tribunal is investigating if there was a campaign to discredit Sgt McCabe by the force.
Mr McGuinness said at the time that there were efforts to stop a probe into the penalty points system. However, having met Sgt McCabe, who denied the abuse allegations, he decided to proceed with the committee’s work.
At a heated PAC meeting on January 23, then garda commissioner Martin Callinan said the actions of garda whistleblowers Sgt McCabe and Garda John Wilson were “disgusting”.
The tribunal heard how Mr McGuinness, after the meeting, went to exchange pleasantries with the garda team, including Mr Callinan. What the garda chief next said “outraged” him, he told the tribunal yesterday.
Mr McGuinness said the commissioner told him about an incident involving John Wilson and a difficulty on Grafton St where gardaí were called.
In the commissioner’s words, Mr McGuinness recalled, Garda Wilson attended an incident, “pulled the knackers off the horse”, got on and rode it back to the garda station.
However, the serving garda chief allegedly said “the other fella fiddles with kids. And this is the type of fucking headbangers I’m dealing with.”
Mr McGuinness took the reference to “other” to be Sgt McCabe.
The alleged conversation happened in earshot of others in the room but was “directed” at Mr McGuinness, the tribunal heard.
Mr McGuinness said he believed this was to “discredit” Sgt McCabe and ensure a future PAC meeting with the whisteblower would not go ahead.
He agreed with Judge Peter Charleton the alleged remarks about John Wilson were designed to “damage” him.
Mr McGuinness said that while he was “deeply troubled” by the remarks, he decided not to follow up on them as further “whispers” could damage the two whistleblowers.
Mr Callinan says only “mundane” matters were exchanged during the chat and argues that what was allegedly said is “outrageous” and “simply incorrect”.
He claims it was Mr McGuinness who called John Wilson a “fucking header”, a claim he in turn denies.
However, Mr McGuinness described how the garda chief then rang him and arranged a private meeting the next day on January 24 in Bewley’s Hotel car park on the Naas Rd, where issues were further discussed.
The garda chief got into the passenger seat of Mr McGuinness’s car and discussed Sgt McCabe.
According to Mr McGuinness, Mr Callinan said Sgt McCabe had sexually abused his family, was not to be trusted, and he had made a “great error” with the PAC.
The TD says the garda chief gave the impression “there was a file”, and action would be taken against Sgt McCabe.
Mr McGuinness said he took notes of this conversation. But ultimately he decided to ignore the garda chief’s claim and instead proceeded with the PAC probe into penalty points “to be fair” to the taxpayer and to Sgt McCabe.
Elsewhere, Mr McGuinness said he was told by Superintendent Dave Taylor, former head of garda press, that he was “used” by garda management to spread rumours to the media about Sgt McCabe.
The tribunal has heard from Supt Taylor that he recalls overhearing Martin Callinan use a term referring to child abuse in reference to Sgt McCabe in January 2014.