As someone who joined the RUC in 1970 as a raw recruit and retired some 25 years later as a detective superintendent and deputy head of CID for Belfast, I've experienced some dark days in the history of the service. However, few can have been as bleak as June 9 this year, when Dr Michael Maguire, the Police Ombudsman, published his findings of the police's conduct in relation to the massacre of the innocents at Loughinisland.
I had known for several weeks that the publication of the report was imminent, but nothing could have prepared me for the exposure of the treachery by some members of Special Branch and the security services.
Losing track of a proportion of the large consignment of weapons smuggled into the province may be partly explained on the grounds that it occurred through a series of unforeseen events, but the withholding of information - and, at times, the misleading of honest CID detectives - is unforgivable and a matter of history repeating itself.
I was at the coalface of anti-terror policing throughout all of my service, and this led me to face-to-face confrontations on the street, or in interview rooms, with some of the most notorious killers of the time, such as Martin Meehan of the Provisional IRA, and Lenny Murphy, the Shankill Butcher.
In the early days of the Troubles, I enjoyed a good working relationship with members of Special Branch, whom I met on an almost daily basis and whom, where possible, I lawfully assisted in every way. At that time, I regarded them as honest brokers in their dealings with me and CID in general. We realised that their primary duty was the recruitment of informants and agents from within all the terrorist groups and that the protection of the identity of these people was essential, especially if they were providing life-saving intelligence.
I will be the first to acknowledge that, throughout the Troubles, Special Branch did a truly superb job, and it's impossible to account for how many lives were saved as a result of their intelligence-gathering activities. Be assured, it could be measured in the hundreds.
However, as the years moved on and many of my contemporaries moved up the Special Branch ladder, I sensed a sea-change in their attitude to CID. They appeared to become more arrogant by the day and, on reflection, these were the first signs of the oft-repeated phrase of them becoming "a force within a force". They seemed answerable to no one but themselves, although most of us realised that MI5 were always shadowing their activities.
During the early 1980s, it was recognised that intelligence-gathering on terrorism in the province was becoming somewhat disjointed, as a result of so many agencies being involved, such as Special Branch, CID and the Army. Consequently, an MI5 officer, Patrick Walker (later to become Sir Patrick Walker and overall head of MI5) was appointed to carry out a review of intelligence-gathering.
He prepared a report for the Chief Constable, who accepted all his recommendations, the principle one being that no planned arrests were to be made without prior clearance from Special Branch.
The primary reason for this was reasonable, insofar as Special Branch may have had long-running operations in place, and it would have been unfortunate if we in CID disrupted them by searching addresses and arresting suspects.
On two occasions, when the Troubles were at their worst, I was the head of CID in areas of west and north Belfast. Part of my strategy at this time was to constantly disrupt all the terrorist groupings active in my area by carrying out weekly planned arrest-and-interview operations, based on good intelligence.
At any given time, I would have had between six and 10 suspects in detention and under interview. Many confessions and a great deal of intelligence flowed from this.
However, a distinct pattern began to emerge in these early-morning arrests, as quite often we discovered some of the suspects out of bed, dressed, breakfasted and puffing on a nerve-calming cigarette. They had been expecting us and it was obvious that they were Special Branch agents and informants who been warned-off by their handlers.
One may well ask why these suspects just didn't go to an alternative address to avoid us, but it helps an agent's cover if he is seen to be arrested now and again.
I had no option but to tolerate this, but the final straw for me came on the evening of February 12, 1989, when Patrick Finucane was murdered in his home and his wife injured in front of their children.
I dealt with the scene and helped ease Mr Finucane into a body bag. I initiated a conventional investigation into the murder, but before long I got the clear impression that this was not just a typical killing by one of the loyalist murder squads operating in north Belfast. There was more to it than met the eye.
I had several other murder investigations under way at the time, and just the next day another one was added to my list when the INLA shot someone dead in the Orange Cross Club in the lower Shankill.
The killing of Pat Finucane was probably the most controversial of the Troubles and was never far from the news headlines. The family hoped for a public inquiry into the murder, but this was refused. However, in 2011, the Government in Westminster opted to appoint a distinguished human rights lawyer, Sir Desmond de Silva QC, to look into the circumstances of the murder.
In 2012, he published his report, which was extensive, and, to the surprise of many, he had been given access to relevant Special Branch reports of the time.
His conclusions were quite clear, in that he found "agents of the state" - or, to be more precise, Special Branch agents - had carried out the murder. To coincide with the publication of the report, Prime Minister David Cameron stood up in the House of Commons and apologised profusely for the involvement of agents of the state in carrying out such a crime.
Although I had my suspicions about this for many years, I was horrified to see the treachery of a few Special Branch officers, and how they had known all along who had carried out the killing, laid out in black and white in de Silva's report.
I was deeply shocked to recall one senior Special Branch officer visiting me in the Finucane incident room in the days immediately after the murder, looking solemn-faced, yet at the same time he knew how and by whom the murder had been carried out.
I was quite staggered that he felt he owed more loyalty to a UFF murder gang than to me, when I was heading up a hard-pressed CID murder investigation.
At the time of the killing of Pat Finucane, some in Special Branch may have felt this was their finest hour, but as the years rolled on, I hope they realised it was but a pyrrhic victory. For example, two of my most trusted CID detectives - Johnston Brown and Trevor McIlwrath - cracked the case by persuading the principal gunman, UFF assassin Ken Barrett, to divulge his role in the killing. He was later convicted, but under the terms of the Good Friday Agreement, he served just two years' imprisonment.
The main Special Branch agent, William Stobie, a UFF quartermaster, who supplied the guns used in the murder, was shot dead by his own organisation, as they feared he was about to give evidence against some of them.
Then, the UFF member whom we believed was the second gunman in the crime committed suicide by hanging himself from the goalposts of the football grounds in Glencairn.
If such a plot, with all of its treachery and tragedies, was presented as a work of fiction, it would immediately be dismissed out of hand by any publisher as being too outlandish. Yet it really did happen.
I'm not ashamed to say that the actions of a few members of Special Branch have caused myself and detectives Brown and McIlwrath serious health problems since the revelations of their actions in the Finucane case. But, more importantly to the three of us, they have also betrayed the memories of the 319 men and women of the RUC who gave up their lives and the thousands who were injured in the pursuit of peace in our troubled land.
The disclosures in the Police Ombudsman's report into Loughinisland, combined with the Finucane case, will ensure the future revisionists of history will cast the history of the RUC in an ill-deserved cold light.