The commission seeking the body of murdered British soldier Robert Nairac has received no information, its chief investigator said.
The Ministry of Defence's refusal to confirm or deny the former captain's whereabouts was "unfortunate" after unfounded and damaging rumours surfaced about his activities in Northern Ireland during the Troubles, Geoff Knupfer said.
The army officer was abducted by the IRA during an undercover operation in a bar in South Armagh in 1977.
He was one of 16 so-called Disappeared spirited away and secretly buried during the conflict.
Mr Knupfer said: "We have not received any information in his case at all.
"We guess this might be because he was a British soldier and of course because of the damaging allegations that have been made or connected with his name in more recent years.
"This is not about Robert Nairac, it is about his loved ones, it is too late to show any compassion for Robert Nairac unfortunately, this is about his family."
The Ministry of Defence last year told an inquest into the shooting dead of 10 Protestant workmen by republicans at Kingsmill in South Armagh that it was "inconceivable" Capt Nairac was at the scene, debunking a conspiracy theory which has done the rounds for years.
Mr Knupfer works with the Commission for the Location of Victims' Remains (CLVR) searching for the last three outstanding bodies of the 16 "disappeared" by republicans. The other 13 have been found.
The Commission was created by the British and Irish governments after the 1998 Good Friday Agreement to search for the remains of those abducted, killed and secretly buried.
Mr Knupfer said the military's stance of not confirming or denying anything was "most unfortunate" in Mr Nairac's case.
"This was not secret information, his personnel file exists and says where he was at any given time in his career.
"He was clearly not in Ireland on four of the dates (when he had been alleged to be involved in incidents).
"I have interviewed witnesses who can personally vouch for where he was.
"We are comfortable that he was not directly involved in events.
"I am pretty satisfied that he was a junior officer. He had not got the freedom to roam around and run riot."
He dismissed rumours circulated that the soldier's body had been destroyed in a meat processing plant as a distraction.
Mr Knupfer and the commissioners making up the CLVR gave evidence to the Oireachtas Joint Committee on the Implementation of the Good Friday Agreement in Dublin.
He appealed for more information about the missing.
"I genuinely believe that we have never knowingly been misled by any of the information passed to us.
"It has all been passed with the best of intentions, albeit it is inaccurate, but that is understandable given the timescales.
"People who may have been involved in these events 40 years ago have now moved on with their lives and their relatives or families may not be aware of what part they played in these events many years ago when they were young people."