If indeed it happened, the smear campaign against McCabe was a 'flop'
Two key Garda witnesses - Sergeant Maurice McCabe and Superintendent Dave Taylor - have potentially explosive stories to tell.
The version of events from each of them has a common thread - but there are also some important differences in their evidence upon which this major inquiry into our police force now turns.
Supt Taylor will today begin his third tough day in the witness box at Dublin Castle after already facing nine hours of straight questions and then cross-examination on Monday and yesterday. The man who headed the Garda press office from July 2012 until June 2014, has spent his time telling the Disclosures Tribunal how he tried to "ruin" Ireland's most notorious Garda whistleblower, Sgt McCabe.
David Taylor still has a senior job in the Garda traffic division and is based inside the Dublin Castle complex where these hearings are taking place.
Mr Taylor's evidence is that his old boss, former Garda commissioner Martin Callinan, told him to tell journalists and key people in public life that Sgt McCabe's whistleblowing motive was revenge against An Garda Síochána, because he had been investigated in 2006 for sex abuse allegations which were never substantiated.
Supt Taylor insists he acted on the orders of Mr Callinan. But his boss's deputy and successor, Nóirín O'Sullivan, knew and approved of the vilification project. The former commissioners utterly reject his evidence, as do many of the journalists to whom he says he was trying to sell the defamatory messages.
The two central tribunal figures - Supt Taylor and Sgt McCabe - had a rather dramatic meeting in September 2016 when Mr Taylor told much about his campaign against the embattled whistleblower. It was a tumultuous encounter - but Sgt McCabe took notes which he later used for his documented case to this process.
Much of the pair's evidence appears to tally - but there are notable divergences for the tribunal chairman, Mr Justice Peter Charleton, to assess. One is that Sgt McCabe insists he learned that Supt Taylor was texting his calumnious allegations to journalists.
Supt Taylor insists that his campaign was run by word of mouth or in face-to-face meetings.
Another is that Sgt McCabe recalls Ms O'Sullivan being styled "a pusher" in the campaign. But Taylor's evidence is that she knew all about it and gave it her approval.
They seem to concur that, at the time of their cathartic meeting, Supt Taylor was "a man who knew too much". This may have played into disciplinary investigations against the former press office head.
There are some other fundamental conflicts, such as a deposition from Independent TD Mick Wallace, which was cited yesterday, that Ms O'Sullivan "spun in her seat when telling lies". Supt Taylor insists he never, ever, said any such thing.
But Supt Taylor did agree with Judge Charleton that his media campaign against McCabe was "a flop". But he rejected a contention by lawyer for INM, Rossa Fanning, that such a campaign never happened in the first place.