The head of a Northern Ireland veterans group has launched a fresh appeal to find the body of missing Army captain Robert Nairac.
Former soldier Alan Barry is leading calls for more information into the disappearance of the undercover officer.
The Grenadier Guardsman was abducted from a bar in Dromintee in south Armagh in May 1977 before being beaten and killed.
Several appeals have been made to the IRA to reveal where they disposed of the captain's body.
IRA member Liam Townson was convicted of Nairac's murder in 1977.
He served 13 years in prison and was released in 1990.
Mr Barry, who heads the Justice for Northern Ireland Veterans, made the appeal from the Ravensdale area in Co Louth where the soldier's remains are thought to be buried.
"We believe he was taken to this location where he was tortured and murdered," Mr Barry said.
"For whatever reason, over the years there has been a wall of silence about the location of his remains and his former regiment want his remains back and more importantly, his two elderly sisters.
"His parents never had the opportunity to bury their son and we believe it is only right and fitting.
"I keep hearing Michelle O'Neill and Mary Lou McDonald talking about truth, transparency, equality and justice.
"When you keep hearing those words from some of the very people who supported the IRA, it's very difficult to take any credibility from what they say.
"As a veteran in Northern Ireland, when we see one of our own rotting in the ground in a shallow unmarked grave, it does bring into question the sincerity of these people."
Attempts to locate his body have been led by the Independent Commission for the Location of Victims' Remains.
Following his disappearance, claims began to surface linking Nairac to a number of massacres during the Troubles.
The head of the commission's investigation unit Geoff Knuper provided evidence to reject those claims.
Mr Barry added: "They tried to link him to a number of massacres but these were investigated by Geoff who confirmed that Robert wasn't even in the country for four of the massacres.
"I do not believe Liam Townson doesn't know where Robert's body is laying and it's time for him to atone and give some element of compassion so his sisters can bury their brother.
"His body is in woodlands making it difficult to pinpoint a location, so we need some idea of the location.
"I took a walk there at the weekend and it's very heavily dense woodland.
"I believe if his remains are recovered his sisters will want a simple Christian ceremony.
"This won't be triumphalism on our part, it's so wrong his remains lie in an unmarked grave.
"Until Robert's remains are found there will always be a British soldier in Northern Ireland.
"This would be a massive gesture on behalf of the republican movement," he added.