Details of the kidnap and IRA murder of undercover British army captain Robert Nairac are to be revealed by the BBC's Spotlight programme.
Captain Nairac's body was never found
The SAS-trained officer was captured from outside a bar in Dromintee, close to Jonesborough, on May 14 1977.
He was shot dead across the border at Ravensdale, County Louth. Six men were convicted of involvement in the murder.
Captain Nairac's body was never found. The killing remains one of the most notorious of the Troubles.
Thirty years on, Spotlight details - for the first time - exactly what happened that night.
The programme confronts the man who pulled the trigger and hears from others who have never before spoken about the case.
In the investigation, reporter Darragh MacIntyre and producer Brendan McCourt examine what happened to Captain Nairac's body and ask why the IRA will not give it up.
The chief investigator for the independent commission set up to recover the bodies of the so-called Disappeared has seen excerpts of the programme.
Geoff Knupfer said: "It would be fair to say that potentially the information provided is very significant indeed."
In 1999, the IRA said it had no information about the undercover soldier's body and until recently his name did not appear on lists of the so-called "Disappeared".
Nine cases remain unresolved, but while information has been provided about most of those missing, virtually no information has been forthcoming about the three men who disappeared in south Armagh: Captain Nairac, Gerard Evans and Charlie Armstrong.
Mr Knupfer revealed that his team had recently met the Nairac family.
He said: "Members of the family would very much like to have the remains of Captain Nairac recovered and formally buried in a place that they can visit in the future and grieve."
The Hunt for Captain Nairac, a Spotlight special, is on BBC One at 2235 BST on Tuesday 19 June.