What's the difference between a bribe and a shakedown? One involves receiving money for a favour. The other could be construed as receiving money for giving the impression that a favour may be done, or that something which the giver may be entitled to will only be forthcoming if a financial consideration is included.

For instance, Padraig Flynn received 50 grand from Tom Gilmartin in 1989. It wasn't a bribe. He didn't do anything for it. Gilmartin believes that Flynn gave him the impression that he "would remove roadblocks" in the way of the developer's proposal. If so, it was a shakedown, an abuse by Flynn of his position in order to enrich himself, but not one that impinged directly on his decision-making.

Gilmartin was shaken down all over the shop. The former assistant city manager George Redmond and the late Liam Lawlor metaphorically grabbed Gilmartin by his trouser legs, turned him upside down, and shook every last copper out of him.

All of which brings us to Bertie Ahern. He is adamant he didn't take a bribe. He is adamant that he acquired the big bags of cash that barrelled through his accounts by way of dig-outs, whip-rounds and winnings on horses.

Gilmartin alleges that his fellow developer Owen O'Callaghan told him that Ahern was paid 30 grand to block a tax designation for a rival developer. The two men were developing Quarryvale, which became Liffey Valley shopping centre. Green properties, which built the Blanchardstown Centre, was looking for tax designation. If they were awarded designation, it would have given Blanchardstown a major commercial advantage over Quarryvale.

The policy of the Department of Finance was to refuse designation, and that was what happened. Irrespective of whether Ahern received money, it doesn't appear to have impinged on his decision-making.

There is absolutely no evidence that he took a bribe. There is circumstantial evidence that he may have been involved in a shakedown, receiving money from O'Callaghan and others on the vague basis that their interests would receive consideration. The three judges of the tribunal will have to decide whether the evidence is of a standard that allows them to make a finding of fact. Both Ahern and O'Callaghan are adamant that no money passed between them.

There are a number of different threads to the circumstantial evidence. Gilmartin says that O'Callaghan told him at a meeting with bankers that Ahern had assured him there would be no tax designation for Blanchardstown, and that it cost him 30 grand. Gilmartin is vague on dates and the exact circumstances of the meeting.

On 24 March 1994, Ahern met O'Callaghan in Government Buildings. At a meeting with bankers sometime after that, O'Callaghan told them that he had received assurances from Ahern that the tax designation was not going ahead.

On 24 April 1994, Ahern met with a bank official in St Luke's and gave him 30 grand in cash to put in a special savings account. He says this money was from savings he accumulated in cash over seven years when he didn't have a bank account.

An odd deposit

It was an odd deposit. He already had £22,500 in the special savings account. The maximum allowable was £50,000. Why did Ahern not just put in the balance, £27,500, to top up the account. Why was it the round figure of £30,000?

O'Callaghan was formulating plans to build a football stadium in Neilstown at the same time. On 2 August, his lobbyist, Frank Dunlop, delivered a detailed proposal to Ahern's office. Six days later, Ahern made a cash deposit of £20,000 to his daughter's account. This, he says, also came from savings he kept in a safe at St Luke's.

O'Callaghan had a US investment bank on board. Chilton O'Connor was based in Los Angeles and was looking at opportunities in Ireland. On 10 November, their representative met Ahern to lobby for the stadium proposal. Ahern says he gave them short shrift.

Yet subsequent correspondence suggests that the Yanks were still under the impression that the project might find favour.

On 5 December, £28,792 was deposited to Celia Larkin's account. This, Ahern says, came from his pal, Micheal Wall, who wanted to buy a house in Dublin, which Ahern would rent. The sum deposited equates to $45,000 using one of the exchange rates in the bank that day. Is it another coincidence that American bankers were sniffing around when this deposit was made?

The stadium project, which was dependant on major state funding, was rejected by Ahern. Again, this was in keeping with a recommendation from the Department of Finance.

Eamon Dunphy has told the tribunal that O'Callaghan once told him that he didn't trust Ahern, that the politician took the money but didn't do anything for it.

In Ahern's defence, it could be claimed that the above threads are an artificial construction, stitched together in an attempt to do him damage. Such a defence might hold water if he had reasonable, or even believable, explanations for the deposits to his accounts. Does anybody out there still believe in unlikely whip-rounds and horses?

During his final appearances at the inquiry last week, he reiterated again and again that he got no money.

"In 40 years of politics, I burst a gut working for the public," he said on Tuesday. "I never got a bribe, I never received money from Owen O'Callaghan, Frank Dunlop, Chilton O'Connor or any of these people in any form."

Over the course of the last year, as the evidence has dribbled out, the refrain from many of Ahern's supporters has changed. They don't believe his explanations for the deposit of three times his annual salary to his accounts over two years. But, they protest, he wasn't corrupt.

In this scenario, corruption consists exclusively of the receipt of a bribe to do a specific favour. Perjury isn't corruption. Where do they stand on a shakedown racket, if it is found that that is what occurred? Where do they stand on wholesale tax evasion?

The tribunal now has the unenviable task of compiling a report to do justice to the effort and cost of this investigation.