A High Court judge is being asked to decide the costs of Ian Bailey's failed legal battle against the State.
The former journalist alleged that he had been unlawfully arrested by gardaí investigating the 1996 murder of French film producer Sophie Toscan du Plantier in Schull, Co Cork.
A jury found against him, potentially leaving the 58-year-old with a €6m costs bill for the 64-day hearing.
His lawyers are trying to reduce the bill by claiming the State parties wasted time in unnecessary evidence.
State lawyers have said Mr Bailey can not throw the dice and then complain that he does not want to pay for the bet.