Senior police commanders in Northern Ireland knew of a threat to kill one of their officers but failed to warn him before he was shot dead, an investigation has found.
The high ranking officers also did not inform detectives investigating the murder of Royal Ulster Constabulary Sergeant Joe Campbell of the specific threat, Northern Ireland's Police Ombudsman Dr Michael Maguire said.
The 49-year-old father of eight was shot on the evening of February 25, 1977 as he locked the main gates of the Cushendall Police Station in Co Antrim and died a short time later.
Sgt Campbell's family believe his murder involved collusion between rogue elements of the police and loyalist paramilitaries.
Dr Maguire, who investigates allegations of police misconduct, said evidence of collusion was "inconclusive".
"On the basis of the information available I can neither discount nor substantiate the allegations of a wider conspiracy into the murder of Sgt Campbell," he said.
But the ombudsman said if senior management in the Royal Ulster Constabulary had ensured an appropriate response to concerns raised about the officer's safety the murder could have been prevented.
"I have to conclude that Sgt Campbell, a dedicated community police officer in the Glens of Antrim, was failed by senior members of the police service of which he was a respected member," he said.
"There is sufficient, reliable evidence that senior police officers throughout the RUC's command structure, including the then Head of Special Branch and quite probably the Chief Constable, were aware of concerns, which had been documented, about a threat to his life and failed to act upon them.
"They should have responded to the threat in a far more robust way. Sgt Campbell should have been warned, which would have allowed him to vary his routine. Police could have mounted visible police patrols in the area and if necessary posted him to an area where the threat would have been diminished or removed. None of this was done."
The RUC chief constable at the time of the murder was Sir Kenneth Newman, who went on to become Metropolitan Police Commissioner. He told Dr Maguire's investigators he had no recollection of the Sgt Campbell case.
In 1980 a member of the RUC's Special Branch and a man identified in court as a police informant were arrested and charged in connection with the murder. The police officer was acquitted and the man was convicted of withholding information in connection with the murder.
The former police officer was re-arrested five years ago in the wake of the ombudsman office probe but the Public Prosecution Service directed that no action be taken.
Dr Maguire said former RUC officers and others interviewed during his office's investigation provided a picture of mounting concern for Sgt Campbell during the mid 1970s.
Investigators spoke at length to one of the police officers who served in Ballymena Special Branch at the time. He told them in detail about the specific concerns he had for Sgt Campbell's safety. He said that such were his fears that he contacted the then de facto head of RUC Special Branch, a detective chief superintendent.
He said he and a colleague had a series of meetings with this senior officer, during which they provided him with reports which outlined their suspicions, including that "Joe was to be lined up to be murdered".
This officer said they arranged another meeting with the detective chief superintendent a number of months before the shooting, at which he assured them the chief constable had the matter in hand.
Another former Ballymena Special Branch officer told investigators that one of these officers raised the issue of Sgt Campbell's safety with a detective superintendent at RUC North Regional Special Branch headquarters. This senior officer declined to assist the Police Ombudsman's investigation.
The police officer who led the 1980 investigation into Sgt Campbell's murder also confirmed to investigators that these two officers and another officer had been submitting reports about the potential risk to the sergeant.
A former detective chief inspector, who had just been posted to Ballymena at the time of the murder, said that when he first arrived, two of these Special Branch officers told him of their fears and that they had submitted reports detailing their concerns.
He told Police Ombudsman investigators he believed that the then chief constable and the detective chief superintendent, who was de facto Head of Special Branch, knew of the risk to Sgt Campbell.
A retired assistant chief constable, who had an administrative role in Special Branch headquarters at the time, confirmed to investigators that this detective chief superintendent had concerns about the conduct of an officer based in Ballymena and of a police informant.
Investigators also spoke to former Army personnel who said they were aware of the risk to Sgt Campbell and passed this information on to police in Ballymena.
An initial investigation into Sgt Campbell's murder proved fruitless and a fresh inquiry was undertaken in 1980 after pressure from his family for action.
Dr Maguire's report identified a number of significant failings in both these investigations, claiming that all available information was not passed to the detectives.
Police Ombudsman investigators saw a statement from a senior police officer who was tasked by the new chief constable with making confidential enquiries into elements within Ballymena Special Branch. That statement said: 'There was specific information available regarding those responsible for Sgt Campbell's murder'.
The investigators also spoke to a police officer who had made a report which said there was a link between a bank robbery in Cushendall in early February 1977 and the murder of Sgt Campbell several weeks later.
The detective who led the 1980 murder investigation told Police Ombudsman investigators that he had not seen either document.
During this murder investigation a team searched a premises linked to one of the suspects and recovered RUC intelligence documents which cannot now be found.
Dr Maguire said the fact this and other material, including the 1977 murder investigation files, are no longer available caused him concern.
"The intelligence reports recovered during the murder investigation may have assisted in supporting or disproving the allegations against those suspected of involvement in the murder," he said.
"That they simply 'evaporated' after being found points to a deliberate act.
"In view of the repeated opportunities presented for the dissemination of the intelligence, it is difficult not to conclude that the material was deliberately withheld from the detectives investigating the murder."
The ombudsman said his overall investigation was hampered by both the refusal of a number of retired senior police officers to co-operate and the loss of police documentation.
Sgt Campbell's son Joe Campbell Jnr, who first lodged the complaint with the ombudsman's office in 2002, said the family's reaction to the report was "mixed".
"We are not particularly pleased that today after 37 years we still don't know from a public official - after two police investigations and an ombudsman's inquiry that lasted 12 years - that nobody in a public office can tell us why our father was killed and who did it," he said.
"What we are very annoyed about and distressed about is the fact the people who were there to uphold the law did the opposite - some of them colluded to murder my father and then them and others within the RUC covered it up to this day.
"There are many RUC officers who came forward and who gave statements to the ombudsman's office and we have to rely that most of those statements were everything they knew, but there were very senior officers who refused to co-operate.
"We find that distressing and feel that like-minded people across this province will find that shocking.
"The people who are paid to uphold the law have refused to do so."
Mr Campbell said the family's campaign for justice would go on.
"Today we have got a report. What we don't have, we don't have the truth and we certainly don't have any justice," he said.
"We know who it was, there are ex-officers out there who know who it was, there are other people who know who it was and why it happened and those people choose not to tell the truth about it and they will have to answer as to why.
"We are not going to go away. We will have to sit down in a measured approach and look at what the report says and the conclusions. Anybody reading the report can only be shocked about it.
"Given that at this moment we don't know from officialdom who did it and why they did it, our quest for justice will continue along with the hundreds of other people out there who don't know what happened to their loved ones."
He urged politicians at Stormont to sit down and "stop bickering" and deal comprehensively with legacy cases related to the past, otherwise he said it was difficult to see peace and reconciliation in Northern Ireland progressing.
In response to the Police Ombudsman report, Police Service of Northern Ireland (PSNI) deputy chief constable Alistair Finlay conceded it made for "difficult reading".
"We note the comments made by the Police Ombudsman and acknowledge his findings around the investigation into Mr Campbell's death in 1977," he said.
"On behalf of the Police Service of Northern Ireland, I wish to express my profound regret at the loss of a highly esteemed colleague in such tragic circumstances and extend our sincere sympathies to his family.
"The Ombudsman report makes difficult reading. It is clear there were significant shortcomings in the RUC handling of information prior to the murder and in both subsequent police investigations into Sgt Campbell's murder. And for that, I am truly sorry.
"Policing back in 1977 operated in a very different context. The RUC's strength as at December 31 1976 was 5,253 police officers, with the service investigating 112 Troubles-related murders the following year (1977).
"Furthermore, intelligence handling, training and investigative standards for detectives, forensic opportunities and family liaison processes were very different to those rightly expected today.
"None of this seeks to excuse any inadequacies or failings in the actions of the RUC. It is simply to place them in the wider context of the time.
"Policing has developed enormously over the past 35 years. With the advent of the Human Rights Act 1998 and other related legislation, PSNI now have greatly improved policies and procedures which guide our response to potential threats and how we approach criminal investigations, compliant with the European Convention on Human Rights.
"It is, however, disappointing to note that a number of retired officers felt unable to engage with this Police Ombudsman's investigation. Although some may have sadly died or are in poor health, the information and assistance from those capable of giving it may have provided a clearer understanding and insight into the events of February 25 1977.
"Finally, one of the key functions of any police service is to bring to account those responsible for such a terrible crime. It is a deep regret that in this case that has not yet been achieved.
"Today, with the publication of the Police Ombudsman's report, details of this murder are fresh in people's minds, I would make a renewed appeal for the people who know who did this to come forward to us with information."