Senior RUC officers were aware of a specific threat to Sergeant Joe Campbell but failed to warn him about it - which could have prevented his murder - according to Police Ombudsman Dr Michael Maguire's report.
It summarises an investigation into events connected to the murder of the Catholic Sergeant, who was shot on the evening of 25 February 1977, as he locked the main gates of the Cushendall Police Station in Co Antrim and died a short time later.
Dr Maguire said more than 30 retired RUC officers, from the ranks of Constable to Assistant Chief Constable, spoke to his investigators as part of the review.
"I have to conclude that Sergeant 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 commented.
They should have responded to the threat in a far more robust way.
Dr Michael Maguire, Police Ombudsman
He continued: "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.
"Sergeant 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."
Former RUC officers and others explained to the Ombudsman team that they had raised specific concerns about the safety of Sgt Campbell, a 49-year-old father-of-eight.
A former Ballymena Special Branch officer told how he and a colleague had a series of meetings with the then de facto Head of Special Branch, a Detective Chief Superintendent, during which they provided him with reports which outlined their suspicions, including that "Joe was to be lined up to be murdered".
He said that in a further meeting, a number of months before the shooting, that they were assured by the senior policeman that the Chief Constable had the matter in hand.
Another former Special Branch officer said he went to a Detective Superintendent at RUC North Regional Special Branch Headquarters - this senior officer declined to assist the Ombudsman's investigation.
The RUC Chief Constable at the time, Sir Kenneth Newman, told Ombudsman investigators he had no recollection of the Sgt Campbell case.
A retired Assistant Chief Constable, who had an administrative role in Special Branch Headquarters at the time, confirmed to investigators a 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.
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.
Dr Michael Maguire, Police Ombudsman
The Ombudsman found significant failings in both the initial police investigation into Sgt Campbell's murder and a fresh inquiry in 1980 - particularly regarding available information that was not passed to detectives.
The report highlights a statement from a senior officer who made confidential enquiries into elements within Ballymena Special Branch, who found that "there was specific information available regarding those responsible for Sgt Campbell's murder".
Another report from a police officer identifies a link with a robbery a few weeks before the killing.
The Detective who led the second murder probe did not see either document. Dr Maguire said the fact that these and other material, including the 1977 murder investigation files, are no longer available causes 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. That they simply 'evaporated' after being found points to a deliberate act.
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 officer was acquitted while the man was convicted of withholding information in connection with the murder.
The police officer was re-arrested five years ago in the wake of the Ombudsman probe, but the PPS directed that no action be taken.
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.
Joe Campbell Jnr, Sgt Campbell's son
Relatives believe loyalist paramilitaries and rogue elements of the police were involved in the murder but the Ombudsman said evidence of collusion is inconclusive.
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.
"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."
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.
PSNI Deputy Chief Constable Alistair Finlay
In response to the Police Ombudsman report, PSNI Deputy Chief Constable Alistair Finlay said the report "makes difficult reading".
He expressed his "profound regret at the loss of a highly esteemed colleague".
He added that policing in this era operated in a very different context but that "none of this seeks to excuse any inadequacies or failings in the actions of the RUC".
"Policing has developed enormously over the past 35 years," DCC Finlay continued.
"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 25 February 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."