He came in with his hands up, and proceeded to lay bare the most shocking depiction of graft and palm-greasing ever seen in Irish politics.
All that was missing - for now - were the names of the councillors and land-owners who handled the brown envelopes.
This was not a story of isolated corruption, of a few errant politicians or developers gone astray. No, here was a system gone rotten to its heart, comprising a web of conniving councillors and land-owners who perverted the planning system for their own ends.
Mr Dunlop spread his net far and wide as he lived up to his promise to "tell all" about the murky background to rezonings by Dublin County Council in the early 1990s. Up to 30 county councillors and 14 land-owners were implicated yesterday in allegations of cash-for-favours detailed by the witness.
Lured by the promise of the massive profits that accrue when agricultural land is rezoned, politicians and land-owners conspired, effectively, to rig votes on the council and achieve the desired result.
Mr Dunlop's role, as the "agent" or "conduit", was central. The land-owners provided him with the "stash of cash" or "war-chest", which he then dispensed to politicians who gorged themselves like pigs at a trough.
The "road map" for this activity was the development plan for Co Dublin, to which changes in land use could be made by a simple majority of the councillors. (Other means of securing a rezoning required a 75 per cent majority.)
It was, as Mr Dunlop said, "a numbers game". There was frenetic activity to ensure that a number of people who were not onside would either come onside or absent themselves, which was as good as a vote.
If councillors had a difficulty being associated with a rezoning in their own area, then efforts would be made to make up the numbers using councillors living farther away, he later explained.
Before Easter, Mr Dunlop told us of payments amounting to £112,000 to 14 different councillors. Yesterday he went much further, detailing additional payments totalling about £75,000. Many of the payments were small three-digit sums, but the total included individual payments of £25,000, £10,000 (twice) and £5,000 (at least twice). Incredibly, payments to one politician are "ongoing".
But there is much more to come. The witness was forced to admit that much of the money channelled into Shefran, his own personal shelf company, went not on personal expenditure - as he had told the tribunal previously - but on payments to politicians.
In addition, he indicated his intention to reveal further payments made to politicians not already dealt with, once he has had the chance to check the council's record of rezoning motions and the development plan. By one estimate, up to £250,000 in potential payments remains to be accounted for.
Mr Dunlop, looking a shadow of the ebullient PR man hitherto known to journalists, came with his lists prepared, clearly anxious to "out" the politicians he once wined and dined.
But first he had to apologise for having withheld vital information from his legal team. This related to the crucial AIB Rathfarnham Road account, used to make the payments to politicians, which he had failed to disclose.
Mr Dunlop accidentally mentioned the existence of this account to his lawyers earlier this year, and they forced him to disclose it to the tribunal. Thus began his downfall.
Even with the protection of anonymity, many of the scenarios would be instantly recognisable to the people concerned, and even identifiable by keen observers. Take the following examples:
£10,000 was paid to Mr Dunlop by an individual with "very long political connections across the political divide" in relation to lands in north Co Dublin. This individual did quite a substantial amount of the work himself, including lobbying councillors. The lands were rezoned.
£5,000 paid, also for northside lands. The rezoning of these lands was the subject of intense opposition by a "State entity". "Strong words were used" and there was significant opposition.
However, the case was promoted by "a political entity one wouldn't normally regard as being involved in rezoning".
£25,000 was paid in cash in relation to lands in south Dublin, near Dun Laoghaire-Rathdown. Two people promoted the rezoning, though there was always a suspicion that another person was involved as a "sleeping partner". The rezoning motion at Dublin County Council was defeated by one vote.
Mr Dunlop explicitly linked the money he paid to most councillors to their support for various rezoning motions. However, he noted: "People were clever enough to indicate the necessity to make preparations for elections."
Expect to hear this response when the politicians are called to give their side of the story.
In most, but not all, cases, he said, his clients were aware of the payments being made to politicians.
Some of the politicians identified by Mr Dunlop as recipients tried to contact him after his first spell in the witness-box, and not all their messages were the sort you would welcome. But for now, Mr Dunlop has performed his service and it is up to the tribunal to delve into this ever-thickening intrigue.