Prosecutors are seeking a maximum 20-year sentence for an Irishman who allegedly tried to buy weapons in Lithuania for a dissident IRA group.
Michael Campbell, 38, was arrested three years ago in the Baltic state in an international sting operation with Irish police.
The alleged dissident republican was reportedly caught giving 10,000 euro to an undercover Lithuanian agent posing as an arms dealer.
"Michael Campbell is accused of serious crimes, and we have solid proof of his guilt," prosecutor Gedgaudas Norkunas said after a closed court hearing in the capital Vilnius.
"All our witnesses have already been questioned by the judge, and we believe this trial is nearing to an end," the prosecutor said.
Ingrida Botyriene, Campbell's lawyer, said: "I think prosecutors are making hasty judgments on the defendant's guilt."
In the past, she has criticised the judge for accepting taped testimony from undercover agents and the slow pace of the trial.
Prosecutor Norkunas said Campbell, from Dundalk, has been given the opportunity to defend himself but has so far refused, saying he wanted to testify at the trial's end.
The next hearing is scheduled for mid-February.
Campbell served a four-month prison sentence in the Netherlands in 2004 after being convicted of smuggling millions of counterfeit cigarettes into Ireland, a major criminal racket run by the Real IRA.