The commission set up to find the bodies of The Disappeared has issued an appeal for help to find the remains of murdered British soldier Robert Nairic.
The army officer was abducted by the IRA while on an undercover operation in a pub in South Armagh in 1977.
It is believed he was beaten and then shot dead.
Remains of 12 of the 16 Disappeared have so far been recovered.
The Commission for the Location of Victims Remains was established by the British and Irish governments after the 1998 Good Friday Agreement to search for the remains of those killed by republican paramilitaries and secretly buried during The Troubles.
The BBC understands IRA members along the border, where Robert Nairac was abducted and killed, have been reluctant to provide information to the commission.
In a statement today, the Commission's Chief Investigator, Geoff Knupfer, said of all the victims, the Commission had the least information on Capt Nairac.
"The Disappeared came from a range of backgrounds but what they all have in common is that they have grieving families who had to bear the additional terrible burden of years of not knowing where their loved one was buried," said Mr Knupfer.
He added: "In the past year or so we have recovered the remains of three of the Disappeared - two of whom had been missing for over 40 years.
"We were able to do that because we were given the information necessary to put us in the right place.
"We need that information to help find Robert Nairac," he said.