The commission in charge of finding paramilitary victims spent "months and months and months" in negotiations with French authorities before being allowed to search for the body of a Newry man, it revealed yesterday.
French authorities have agreed that INLA members will not be prosecuted for murdering Seamus Ruddy, who was abducted in Paris in 1985.
The Independent Commission for the Location of Victims' Remains (ICLVR) has started a detailed search for his body in a half-hectare site in a forest near Rouen in northern France.
It follows months of meetings with national, regional and local government officials and police, as well as French prosecutors, forestry officials and many others.
Geoff Knupfer, the lead investigator of the ICLVR, said the French authorities were placed in a unique and difficult legal situation.
"It took months and months and months of talks. The French are not interested in prosecuting the case. They have a statute of limitations on some offences and they say that INLA members will not now be charged with murder," he said.
The search in France is also a unique legal position for the ICLVR, which has been tasked with finding the remains of paramilitary victims, most of whom were buried in the Republic.
Legislation on both sides of the border prevents the ICLVR, the gardai and the PSNI from recovering any forensic evidence from the burial sites if the paramilitaries involved give information about the whereabouts of their victims remains.
France is not covered by the legislation and former INLA members were concerned that they could be prosecuted for murder if they revealed where Mr Ruddy is buried.
It's believed that there has been extensive discussions between the ICLVR and former INLA members, who are being advised by the republican paramilitary group's political wing, the Irish Republican Socialist Party (IRSP).
About ten workers from a Monaghan civil engineering firm are in France to assist with the search. Anne Morgan, Mr Ruddy's sister, has visited the forest at Pont-de-l'Arche outside Rouen, where fresh searches began this week.
Jon Hill, from the commission, said the operation could last for a month.
Meanwhile, a leading member of the IRSP said there is widespread regret within the republican socialist movement over the murder and secret burial.
Strabane-based Willie Gallagher told the Belfast Telegraph: "Of course there is (regret) and that applies to all of those who were disappeared during the Troubles. Disappearing people is getting into the realms of war crimes. It was not an INLA policy to do this, it was a one-off. But, that is in no way an attempt to justify what happened."
Anyone wishing to contact the ICLVR can do so by calling 00800-555 8550 from Britain or Ireland or on 00353 1 602 8655 from abroad.