Ian Bailey will find out today if he is to be extradited to France over the killing of Sophie Toscan du Plantier in west Cork 15 years ago.
The Supreme Court in Dublin will rule if Mr Bailey can be sent for questioning about the killing of the French film-maker.
Irish law dictates the 54-year-old former journalist should only be extradited to face prosecution.
Ms Toscan du Plantier, 39, was found beaten to death outside her holiday home in Schull two days before Christmas 1996.
Mr Bailey, a one-time suspect in the investigation here, has always protested his innocence. He was arrested twice but never charged by the Director of Public Prosecutions (DPP).
Paris-based investigating magistrate Patrick Gachon was appointed by authorities in France in 2008 to run an independent inquiry into Ms Toscan du Plantier’s murder.
A European Arrest Warrant was later issued for Mr Bailey, who has been fighting his extradition for almost two years.
Lawyers for the Manchester-born former journalist, who still lives in Schull, have always maintained there are no grounds to extradite him.
The recent law graduate took his appeal to the Supreme Court last month, where it emerged no decision had been made to charge Mr Bailey in France.
The five-judge Supreme Court reserved judgment on the matter, along with two other points of law opposing the extradition order.
Barristers argued France should have no right to exercise extra-territorial jurisdiction over Ireland, if Ireland could not do the same in a reverse scenario.
They also maintained his client should be treated under the European Arrest Warrant Act 2003, which specified a person should not be surrendered if the offence was committed outside the issuing state of an arrest warrant. The Act was amended in 2005.
Elsewhere, Mr Bailey’s legal team indicated that should the judges’ rule against all three points, they will present further evidence indicating that the Garda investigation into Ms Toscan du Plantier’s murder had been mishandled.