Vital intelligence reports about the threat to a policeman who was subsequently murdered were lost twice by the RUC – and have never been recovered, it can be revealed today.
Sergeant Joe Campbell was shot dead in 1977 as he closed the gates of Cushendall RUC station. It has always been believed that the murder involved a rogue police officer.
The existence of the intelligence – some of it classified 'Top Secret' – and its loss was never made known to prosecutors, who failed to secure a conviction.
Denis Murray, the former RUC Special Branch officer who supplied the sensitive intelligence, is now demanding that the Police Ombudsman tracks down whoever leaked it.
"Some of this information was coming from high command within the Provisionals. When you were handling sources at that level you knew what the consequences of any slip-up could be – death of the source," said Mr Murray.
They included reports of conversations he had with Mr Campbell about a suspected threat to Mr Campbell's life from a rogue RUC Special Branch officer. They also included reports from one of the rogue officer's paramilitary contacts, who claimed he was under pressure to murder Mr Campbell.
In their last meeting, Mr Murray warned Mr Campbell that a confidential source had informed him of a threat involving a police officer to murder him.
"Joe was visibly shaken. He was shocked and whenever we went on to talk about it he told me he wasn't altogether surprised," Mr Murray said.
Mr Campbell believed he was under threat because he was probing robberies in which he believed an RUC officer had co-operated.
At the time, Mr Murray and a colleague were passing on information on the threat to Michael Slevin, the acting head of Special Branch.
Chief Superintendent Slevin told him it was stored in a safe in the office of the then Chief Constable Sir Ken Newman. But when Mr Campbell was murdered it was found to have disappeared.
Much of it was later recovered from a shed in Gracehill near Ballymena, alongside an illegally held rifle.
Shortly afterwards it disappeared again. The Belfast Telegraph has seen evidence that its existence was never made known to the prosecuting authorities.
When attempts to prosecute failed, Mr Campbell's family made a complaint to the Police Ombudsman and an investigation started around 2002. Mr Murray was one of its main sources of information.
In 2009 Mr Murray made his own complaint to the Ombudsman about the second disappearance of the papers. He was told that the complaint was out of time but that a senior investigator was trying to get it investigated as a "grave" and "exceptional" matter.
"I want a police officer to be held responsible for the disappearance of these documents," said Mr Murray. He named three he felt had questions to answer.
"The Ombudsman's report has now wound up but I think they should be looking at where these documents have gone, at what stage they disappeared, why they disappeared and who was responsible," he said.
An Ombudsman's spokesman confirmed that the documents had disappeared twice, as Mr Murray described, and that they were still missing.
Sergeant Joe Campbell, a Donegal-born Catholic, was posted to the Glens of Antrim in 1963. Before his murder in 1977 he told Denis Murray, a Special Branch officer, that he feared fellow officers he suspected of corruption were plotting to kill him.
Three years after Campbell's death one RUC officer, Charles McCormick, was acquitted of his murder.
Last month Michael Maguire, the Police Ombudsman, concluded that Sgt Campbell's life could have been saved. He was highly critical of previous police investigations into the murder, saying they failed the bereaved family.