Fresh evidence in Ian Bailey's fight against extradition to France for questioning over the murder of film-maker Sophie Toscan du Plantier is to be heard at Ireland's highest court.
The one-time suspect won a legal challenge to have recently released state documents admitted as part of his appeal.
The former journalist from England, living in Schull, west Cork, is wanted in Paris for questioning over the 1996 murder.
The five-judge Supreme Court ruled the new evidence claiming the murder probe was flawed and prejudicial will be part of a three-day appeal. But they rejected his barrister's application for the entire case to be reheard in the High Court.
Mr Bailey's extradition was ordered by the High Court last summer.
The 54-year-old's legal team had applied for the courts to have access to state documents which say the original criminal investigation was tainted by "garda misbehaviour of the lowest standards".
The new material was provided by the State to Mr Bailey's lawyers last November and included a 44-page critical review of the conduct of the murder investigation and the reasons why the former director of public prosecutions (DPP) decided not to prosecute.
It came to light when Eamonn Barnes, now retired, emailed authorities dealing with the extradition to tell them about the existence of his 2001 review.
Last week, the court heard Mr Bailey's legal team had been told the Attorney General, Marie Whelan, felt the material was "very significant" and may be something Mr Bailey will rely on. Justice Minister Alan Shatter believed that in the interests of justice they should have it, the court was told.
The 39-year-old's body was found near her holiday home in Schull on December 23, 1996. Mr Bailey denies any involvement with the murder of Ms Toscan du Plantier. He was arrested and questioned twice by gardai, but no charges were ever brought.