Michael Campbell, the brother of a senior Real IRA figure in Ireland, was arrested in January 2008 when he allegedly handed euro10,000 (then $14,000) to an undercover Lithuanian intelligence agent posing as a weapons supplier.
Campbell's lawyer, Irena Botyriene, told reporters she asked the judge to dismiss the prosecutor, Gedgaudas Norkunas, for violating her client's rights by allowing police to interrogate Campbell without a lawyer present.
The Vilnius court did not permit reporters to attend Wednesday's session, the first since both sides made opening statements two months ago.
But the court issued a statement saying it was considering both Botyriene's complaint and a rival application from prosecutors, who want authorities not to permit Campbell to make telephone calls back to Ireland. The prosecutors contend that Campbell would try to pass messages to the outlawed Real IRA.
Campbell, 36, would face up to 20 years in prison if convicted of seeking weapons for terrorist purposes.
The Real IRA was responsible for the deadliest attack of the entire four-decade conflict over Northern Ireland: the August 1998 car-bombing of Omagh that killed 29 people, mostly women and children.
Campbell's brother Liam was a founder commander of the splinter group, which was formed in 1997 to oppose the IRA's cease-fire declared that year. He has already served a prison sentence in the Republic of Ireland for Real IRA membership and is currently in jail in Northern Ireland awaiting potential extradition to Lithuania over his alleged part in the weapons-smuggling effort.
Today the Real IRA continues to plot bombings and shootings in hopes of undermining Northern Ireland's Catholic-Protestant government and sparking a return to wider violence. Its most recent attacks include the March killing of two off-duty, unarmed British soldiers as they collected pizzas outside an army base.