Former Sinn Féin councillor Jonathan Dowdall had "an incredibly powerful incentive" to give evidence against his co-accused Gerard Hutch because a charge of murder against him was dropped, the Special Criminal Court heard today.
The prosecution insists, however, there was never any link between the two events.
Mr Hutch and Dowdall were both charged with the murder of Kinahan gangster David Byrne at the Regency Hotel on 5 February 2016.
However the murder charge against Dowdall was dropped and he agreed to make a statement and give evidence against his co-accused Gerard Hutch.
Mr Hutch, 59, from The Paddocks in Clontarf, Dublin has pleaded not guilty to the murder of Mr Byrne at the Regency Hotel in 2016.
The three judges are to rule on the admissibility of Dowdall's evidence tomorrow.
Mr Hutch claims the dropping of the murder charge against the former Sinn Féin councillor was an "incredibly powerful incentive" and makes it impossible for him to get a fair trial if Dowdall gives evidence.
Mr Hutch's defence counsel Brendan Grehan SC submitted today that Dowdall had the Director of Public Prosecutions "over a barrel", and had engaged in a "very careful choreography" to ensure that only after his murder charge was dropped did he commit to making a statement in writing.
It was he said clear, there was a "quid pro quo".
But the prosecution said today that the DPP had made the decision to drop the murder charge and replace it with a lessor charge which Dowdall is now serving four years before he had made any statement.
"Once Jonathan Dowdall has that acceptance" prosecution counsel Sean Gillane said, "he doesn't have to make any statement. He can just get on with things".
"There was," the prosecution insists, "never any link".
It also says that Dowdall should be allowed testify in the case because "the court is entitled to hear the evidence of every man".
It is the State's case that Jonathan Dowdall met Gerard Hutch a number of times after the murder and that Mr Hutch told him he was "one of the team" that murdered David Byrne at the Regency Hotel in 2016.
The three judges will rule tomorrow on the admissibility of Jonathan Dowdall's evidence and therefore on whether or not he will be allowed testify against his former co-accused.