On the evening of Monday 8 January 1990, a group of British detectives decided that they had done enough for one day. It was getting late now, and some of the officers had been working for thirteen hours on a complex and politically fraught investigation that was being conducted against a backdrop of escalating violence.

Northern Ireland’s savage little war had just entered its twenty-second year. Eighty-nine people had died the previous year. One, Pat Finucane, a lawyer, had been shot fourteen times after gunmen used sledgehammers to smash down his front door while he was having Sunday dinner with his wife and three children. Another was Loughlin Maginn, a father of four who was shot dead at his home in a village south of Belfast. It was the circumstances surrounding these murders, along with a string of others, that the police team led by John Stevens were investigating. At just past 9 p.m. they flicked off the lights of their incident room, locked up, and left the building.

The facility from which they were working was no ordinary police station. It was located beyond the chain-link fences, the razor wire and the CCTV that protected a seventeen-acre complex that the Royal Ulster Constabulary (RUC) operated on the outskirts of Carrickfergus, a coastal town twelve miles north of Belfast. Known as Seapark, the complex was home to forensic science laboratories, exhibit stores, a suite of offices and no end of confidential archives. It was one of the most secure policing facilities anywhere in the world.

Twenty minutes later, four members of Stevens’ team who had been conducting inquiries elsewhere arrived back at the incident room, intending to lock some paperwork away for the night.

First they smelt the smoke. Then they saw the flames. The entire incident room was ablaze and they rushed to raise the alarm. Sarah Bynum, one of the detective constables, later recalled: ‘There were a number of fire alarm points in the building and I went to one and I smashed it with the heel of my shoe and nothing happened. I ran down to another one and smashed that and again nothing happened.’

A heat-sensitive intruder alarm had also failed. Bynum raced to the guardhouse at the entrance to the complex, where an armed officer from the RUC was on duty. ‘My first word to him was to call for the fire brigade and he replied that the phones were down. I then told him to get on his radio to call for help and his reaction was one of almost disinterest, of: “Well what do you expect me to do about it?”’ By the time the fire was eventually extinguished, the team’s desktop computers had melted into pools of metal and plastic; steel filing cabinets had buckled, and the documents inside had incinerated.

Whoever started the fire clearly intended to destroy every scrap of documentary evidence that the police team had gathered.

The immediate suspects were not members of one of Northern Ireland’s paramilitary groups, however, but British soldiers. Stevens and his team were convinced that the arsonists were from the Force Research Unit - a shadowy British Army Intelligence Corps body known as ‘the FRU’ that worked closely with MI5 and Special Branch, the intelligence wing of the RUC. They also suspected that detectives from Special Branch had helped the FRU to slip into the high-security complex and break into their office.

This remains their belief a quarter of a century later. While an RUC investigation concluded that the fire had been started by accident, John Stevens, now Lord Stevens, is of a different view: ‘This incident, in my opinion, has never been adequately investigated and I believe it was a deliberate act of arson.’ Later, Stevens would look back on his investigation and lament that ‘in almost thirty years as a policeman I had never found myself caught up in such an entanglement of lies and treachery’.

It is unclear how much harm was caused to Stevens’ investigation by the fire. Stevens says he had been warned that an attempt would be made to sabotage his inquiry, and had established a ‘duplicate office’ at the headquarters of the Cambridgeshire police. However, a senior member of his team, Detective Chief Superintendent Laurie Sherwood, says some written statements and exhibits could not be recovered.

What is clear is that both the FRU and Special Branch would have been anxious to see an end to Stevens’ investigation: they knew that if he pressed on it would be only a matter of time before he stumbled upon the true nature of the British govern-ment’s role in the Northern Ireland conflict. A few hours after the incident room at Carrickfergus went up in flames, Stevens and his team had been due to arrest one of the men they believed to be behind the killing of Pat Finucane and Loughlin Maginn. That man, a former British soldier called Brian Nelson, was also known as Agent 6137: he was working for the British government.

Nelson had been placed on the payroll of MI5 and inserted, by the FRU, into the Ulster Defence Association, a loyalist para-military organisation. By the time Stevens and his team were about to come calling he had, by his own account, been involved in eight murders, two attempted murders, thirty-four conspiracies to murder and several other serious offences.

In linking Nelson to the Finucane murder, Stevens’ detectives were not merely solving a single crime - they were, in Stevens’ words, about to uncover ‘something extremely dangerous and difficult’ - namely, the evidence that the British state had been operating a death squad in Northern Ireland. It wasn’t pulling the triggers of that squad’s guns, perhaps, but, through Nelson - and others - it was pulling the strings of those who did.

For a generation, the overwhelming majority of the British people had regarded their armed forces as reluctant peacekeepers between two warring tribes in Northern Ireland, and had seen themselves as the innocent victims of a terrorist campaign. That narrative would be seriously undermined if it were to become clear that the British state was influencing, or even managing, the actions of the gunmen from one of those two tribes - if it were to emerge that elements within the British security forces had not merely begun to mirror the terrorists, but were in control of terrorism - and had been, almost from the beginning.

The appalling acts of the paramilitaries were, with some notable exceptions, acknowledged at the time they were committed, even if some today insist they were committing ‘political’ rather than ‘criminal’ offences. But some of the actions of soldiers and the police continue to be concealed or denied, particularly those acts that led to loss of life. Even more painstakingly hidden is the extent to which the state, through its proxies like Agent 6137 Brian Nelson, was orchestrating acts of terror.

Attempts to investigate such crimes all too frequently face obstruction, with the government failing to disclose material it holds that would allow the truth to be established; inquests, Ombudsman’s inquiries, litigation and police reviews have dragged on for decades.

There is a suspicion among some in Northern Ireland that the British state is unable to contend with the past because it cannot disclose the full truth, in all its intricacies.

In 1980, a major new initiative was launched in the secret intelligence war against the IRA after Jack Hermon was appointed Chief Constable of the RUC. Hermon was sworn in on 2 January, amid carnage. The previous day, three people had been killed. On the day of the ceremony a fourth died, and then two more. By the end of the week the death toll had reached nine, as three members of the Army’s Ulster Defence Regiment, one a twenty-one-year-old Catholic, were blown to pieces when their Land Rover drove over a one-ton IRA bomb.

Hermon had been a serving police officer for thirty years and Deputy Chief Constable for almost four, time enough to come to the conclusion that the RUC had become overly reliant on interrogation. He was of the view that securing convictions by beating confessions out of suspects was a disastrously counter-productive practice, as it had engendered deep hatred of the security forces among nationalists, and may have prolonged the conflict. He was also concerned that the reports about the brutality inside the police holding centres had damaged the reputation of the force.

Hermon believed that a subtle intelligence-gathering apparatus needed to be developed, in which information would be supplied not only by informants recruited from within the IRA and the other paramilitary groups, but also by agents inserted into their ranks. Senior British intelligence officers in the province, and Lieutenant General Sir Richard Lawson, the newly appointed Army commander, appear to have shared this view.

During the first week in his new job, Hermon asked the Irish Joint Section, the combined MI5 and MI6 organisation then operating in Belfast, to look into the issue and produce a report. The work was carried out by Patrick Walker, soon to become the most senior MI5 officer in the province and, by the end of the decade, Director General of the agency. Walker spent several months examining the options before producing a report which was to have far-reaching implications, both for the future shape of the British state’s counter-insurgency operations in Northern Ireland, and for the relationship that some detectives and intelligence officers in the province would have with the rule of law.

Walker’s recommendations have never been made public, but the confidential RUC memorandum that ordered their implementation has since surfaced. In February 1981, Assistant Chief Constable John Whiteside wrote to all officers between the rank of inspector and chief superintendent serving with the RUC’s Criminal Investigation Department (CID) to inform them of the recommendations contained within what he termed the ‘Walker Report’. Whiteside explained that these had been approved by Hermon and would come into force in one week’s time.

The CID’s detectives were responsible for detecting criminals; the Special Branch detectives were responsible for gathering intelligence. Whiteside’s memo ordered that all informers pro-viding information on ‘subversive crime’ and ‘non-subversive crime’ would henceforth be handled by Special Branch, whenever possible.

Critically, members of paramilitary groups who had been recruited as informants were not to be arrested - regardless of the crimes that they had committed - without consultation with Special Branch: ‘All . . . planned arrests must be cleared with Regional Special Branch to ensure that no agents of either RUC or Army are involved.’ Any decision to charge an agent with an offence ‘must be the result of a conscious decision by both Special Branch and CID in which the balance of advantage has been carefully weighed.’ The Walker Report is said also to have stipulated that records should be destroyed after operations.

The RUC’s Chief Constable had decided, with the en-couragement of MI5, that the gathering of intelligence would take priority over the apprehension and prosecution of people responsible for killings, kidnappings and bombings. And, on occasion, the people who were responsible for these acts would remain at liberty, if they were also working as informants for the police or the Army, and their usefulness to the state was assessed to outweigh the danger that they posed to the public.

This was just the beginning. As the decade progressed, informants were recruited before they joined paramilitary organisations. These individuals would then be given privileged access to selected police and Army intelligence material, which would enable those organisations to select targets for murder.

Police and Army agent-runners were effectively deciding who was to live and who was to die; and while such decisions were being taken, MI5 hovered nearby.

This presented the police with a legal dilemma, as outlined in the minutes of a meeting between senior RUC officers and Northern Ireland Office (NIO) officials from March 1987, which state: ‘The RUC were to a large part dependent on intelligence if they were to be successful in combating terrorism. Such intelligence was obtained by placing/using informants in the middle ranks of terrorist groups. This meant they would have to become involved in terrorist activity and operate with a degree of immunity from prosecution.’

The problem, as the RUC pointed out at this meeting, was that the only guidelines to police work of this nature had been written in 1969, before the conflict began, and ‘were totally unrealistic/unworkable for dealing with terrorism’. In 1988, in a submission to the Northern Ireland Office, an Assistant Chief Constable spelled out the issue in the clearest possible terms: ‘Taking the example of the terrorist informer who has been instructed to conceal munitions in his house to await their being used. Whatever instructions the informer’s handler gives will be “wrong”, in that if he directs the informer to refuse to comply, the latter will automatically become the subject of suspicion (and probable eventual death); if the handler tells the informer to assent, a breach of the guidelines (and probably the law) is involved.’ MI5’s legal advisor, meanwhile, was warning that the fundamental problem with the guidelines was that ‘in order to run a terrorist agent so as to gather intelligence or evidence, they must be continually breached’.

The RUC’s attempts to put its informer-handling operations on a legally sound footing came to nothing. In May 1987, an internal minute to the Permanent Under-Secretary at the NIO said: ‘It would suit us if the process set in train by the RUC makes fairly slow progress. It would not be wise to take any steps at this juncture to halt it; we should simply desist from hasten-ing it.’

A short while later, Raymond White, the head of Special Branch, raised the problem with the Prime Minister, Margaret Thatcher. When she asked whether he needed anything else in order to combat terrorism, White replied that he regarded ‘a sound legislative basis’ as essential for such intelligence operations, rather than the ‘grey area’ in which he was obliged to work.

After some delay, government officials informed him eventually that ‘the issue was too difficult to handle’, and that Special Branch should continue as before. White complained that the government’s response was, in effect, to ‘carry on doing what you’re doing but don’t tell us the details’. The issue came to nothing because government lawyers knew that any guidelines that allowed serious crimes to be committed with impunity by police informers - agents of the state - could never be lawful.

The RUC’s Special Branch was not the only force operating in a legal grey area. The Army’s undercover Force Research Unit handled agents in an almost identical fashion. There were frequent tensions between the two organisations, and some misunderstandings. Special Branch regarded the Army’s sources as being ‘rubbish and of a poor standard’. But they shared this much in common: they were wings of the state that had been permitted to become managers of terrorism as part of a long-term counter-terrorism strategy. And behind both Special Branch and the FRU would stand MI5, offering a guiding hand, a degree of political cover, and the cash to pay to informers.

As a consequence of the implementation of the Walker Report, Special Branch would be compelled to impede some CID investigations - including murder inquiries - if key informers were to be kept out of prison. This no doubt explains why Alan Simpson, the detective who led the initial investigation into the murder of Pat Finucane, says that one of Hermon’s assistant chief constables, Wilf Monahan, warned him at the outset to ‘not get too deeply involved in this one’. Although the Whiteside memo on the Walker Report was read by a great many CID detectives, some appeared not to immediately grasp its implications. An-other Belfast detective was aghast to discover that Special Branch had tipped off a man he was planning to arrest for questioning about the murder of Finucane. ‘They were obviously keen to protect someone,’ he recalled. ‘But who, and why?’

These were the questions that John Stevens’ team of detectives found themselves asking. Slowly, they discovered the answer. Without any public statement, the RUC had been transformed from a force that prioritised keeping communities safe through traditional policing practices, to one that aimed to win a secret intelligence war.

And one of the figures Stevens’ team came to believe was at the centre of this intelligence war was also the prime suspect in the Pat Finucane murder: Brian Nelson.

A thin, nervous-looking man, a drinker and a chain smoker, Nelson was the most unlikely-looking terrorist and intelligence agent: ‘not an inspiring specimen’, according to Stevens. Born in 1947 in the loyalist Shankill district of west Belfast, he joined the Black Watch regiment of the British Army as a teenager, serving in Cyprus and Germany. But his disciplinary record was poor, marked by repeated periods when he was absent without leave, and in 1969 he was discharged.

Back in Belfast, Nelson joined the UDA, and in 1973 was sentenced to seven years in prison for his role in the kidnap and torture of a disabled Catholic man. He was released in 1977, and seven years after that he approached the Army and volunteered to become an informer. The Force Research Unit was put in charge of Nelson and asked him to rejoin the UDA. Over the next seventeen months, Nelson met his handlers around sixty times and was paid more than £2,000 in cash.

Soon he was appointed as the intelligence officer for the UDA in west Belfast, playing a central role in selecting and locating targets for assassination. Although he occasionally kept this information to himself, Nelson would frequently pass details of these planned murders to the FRU. Over the years that followed, the FRU and the police took steps to prevent just two of the intended victims from dying. One of these individuals was Gerry Adams, the senior IRA commander. In the second case, the FRU appears to have intervened only because the UDA’s plans involved Nelson driving the getaway car, which would have put him at risk of arrest.

In June 1985, Nelson embarked upon the most extraordinary operation of his undercover Army career. The UDA’s leadership asked him to help arrange a deal with Armscor, apartheid South Africa’s arms corporation. A unionist from Armagh who had emigrated to Durban and was working for the company had been identified as a possible source of weaponry, and Nelson was asked to meet this man. The FRU not only encouraged him to do this, it paid for his airline tickets to South Africa and met his hotel bills. One of Nelson’s FRU handlers, a man whom he knew as Ronnie, had told him: ‘You’ve really hit the big time here Brian.’ While some have claimed the FRU sponsored this arms-trafficking enterprise in order to intercept the weapons and prevent them from falling into loyalist paramilitaries’ hands, others suspect that the FRU, and some of their political masters, were determined to help arm Ulster’s loyalists.

In Durban, Nelson examined a number of weapons, and was particularly taken with an automatic shotgun called the Striker which ‘could be used to devastating effect . . . in close-quarter combat’. Armscor made it clear that it would accept a cash sale, but also wanted to know whether the UDA could provide it with one of the latest generation of ground-to-air missiles that were under development at Shorts, an aircraft and armaments factory in east Belfast. In the event, no weapons were purchased at that time, with Nelson being told that the UDA had insufficient funds.

A couple of years later, however, the connection Nelson had made with Armscor did bear fruit. Armscor provided weapons to loyalist paramilitaries in a trafficking operation that was financed by a £325,000 robbery from a bank in Portadown, thirty miles south-west of Belfast. The corporation’s European agent, an American called Douglas Bernhardt, had learned that a large cache of arms held by a Lebanese militia in Beirut had come onto the market. Bernhardt arranged for the arms to be loaded into a container, which was shipped to Belfast via Liverpool, accompanied with bills of lading and notes of origin that indicated it held ceramic floor tiles. ‘There were at least a couple of hundred Czech-made AKs - the VZ-58,’ recalls a former Armscor employee who helped to broker the deal. ‘And 90-plus Browning-type handguns: Hungarian-made P9Ms. About 30,000 rounds of ammunition. Plus a dozen or so RPGs and a few hundred fragmentation grenades.’ At every step of the operation, this source says, the UDA’s intelligence officer was kept informed of its progress.54 This was Nelson, the FRU’s Agent 6137.

The weapons arrived at Belfast docks in late December, and were smuggled into the country undetected. Early the following month, at a farmhouse in County Armagh, the arsenal was divided three ways between the UDA, the UVF and a third loyalist paramilitary group, Ulster Resistance. The UDA lost its entire portion within minutes: its share of about 100 weapons was loaded into two hire cars, which were stopped and seized at a nearby police roadblock. Some of the UVF’s weapons were also recovered over coming weeks, but most remained in the group’s hands, and transformed the loyalists’ firepower over the years that followed. The portion that went to Ulster Resistance was never captured, however. Nor were these weapons decommissioned during the peace process: they remain hidden today.

There was an attempt to smuggle a further consignment of arms into Belfast the following year after three loyalists travelled to Paris with a stolen Shorts missile part. They were about to hand it over to Bernhardt and a South African intelligence officer, when all five men were arrested by the French security agency, the DST.

The loyalists and arms dealers involved in this operation are convinced that Nelson knew about both arms-smuggling operations, and assume that he must have informed the FRU. Noel Little, one of the loyalists detained in Paris, says: ‘Brian Nelson was inserted into the UDA as an agent, he wasn’t a recruited member. How could he know about it and not tell his handler?’

Nelson himself would later confirm this, recounting in his journal how one handler, ‘Ronnie’, told him during discussions about his South African adventures that ‘because of the deep suspicion a seizure would have aroused, to protect me it had been decided to let the first shipment into the country untouched’.

As part of his investigation into the murder of Finucane, and the FRU’s role in managing loyalist terrorism, Stevens attempted to discover more about this weapons consignment. Members of his team travelled to South Africa to interview former Armscor officials, but concluded eventually that evidence of a chain of responsibility would remain elusive. However, a senior member of the inquiry team says he believes it feasible that the UK gov-ern-ment could have been involved in bringing the weapons into Belfast - or at least turned a blind eye. ‘It’s not at all far-fetched,’ this senior police officer says.

Whatever the truth about the FRU’s role in the arms-smug-gling operation, the consequence was that loyalists’ access to high-calibre weapons - and their ability to slaughter both republicans and uninvolved Catholics - changed immediately. In the six years prior to the importation of the South African weapons, from January 1982 to December 1987, loyalists killed seventy-one people. In the seven years afterwards, from January 1988 to 1 September 1994, loyalists killed 229 people. Today, loyalists boast that the IRA was forced eventually to ‘sue for peace’ because of the pressure it came under as the killings mounted in the aftermath of the largely successful South African smuggling operation.

By the end of 1985, a few months after his return from South Africa, Nelson had had enough. He resolved to break his links with both the UDA and the British Army’s FRU,60 and took his wife and three children to what was then West Germany. He found work in a small town north of Munich, fitting floors in new buildings.

In February 1987, however, the FRU phoned Nelson and asked if they could meet him. He was flown to Heathrow, where he spent several hours drinking in a hotel bar with a FRU agent handler and an MI5 officer, who persuaded him to return to Belfast and rejoin the UDA as a British agent. He was promised a deposit to buy a new house, a car to enable him to work as a taxi driver, and £200 a week. He would also receive generous bonuses. Even though he was earning more money in Germany, Nelson agreed. From that point until his arrest in January 1990, Nelson was paid a total of £46,428 from FRU funds. MI5 would later tell an official inquiry that it disapproved of Nelson’s re-recruitment. In fact, however, the agency’s own records show that it did want to see Nelson return to Belfast, as long as he could persuade the UDA to appoint him as its intelligence officer.

With the help of the intelligence that was being passed to him by his Army handlers, Nelson quickly achieved this role, becoming the UDA’s senior intelligence officer for the whole of the province. He went to work compiling a card index library detailing the home addresses, workplaces and haunts of suspected members of the IRA. Many of the cards had police photographs attached. Some of the material came from electoral registers and newspapers. Much of it came from montages of the names and photographs of terrorism suspects that were compiled by the police and issued to members of the security forces on checkpoint duty. Some information, such as car numbers, were supplied by his FRU handlers. At one point, the FRU helped him weed out material that was out of date. Copies of the cards would be handed to UDA gunmen prior to an attack, and sometimes they were also supplied to the UVF. The FRU also kept its own copy of Nelson’s entire card index library.

After each of their meetings with Nelson, FRU handlers would complete contact forms detailing what he had said. During one meeting after another, Nelson would express his desire to see the UDA become more ‘professional’; he was anxious to ensure that its violence was directed only towards the IRA. His handlers clearly approved. ‘6137 wants the UDA only to attack legitimate targets and not innocent Catholics,’ they wrote on one contact form. Nelson ‘wants to see an end purely to sectarian murders and to concentrate on specific targeting of legitimate republican terrorist targets’, said another. Nelson’s appointment as an intelligence officer ‘enables him to make sure that sectarian killings are not carried out but that proper targeting of PIRA [Provisional IRA] members takes place prior to any shooting’, noted a third.

As well as the information supplied by the FRU, Nelson and other members of the UDA were receiving material from other soldiers and police officers. In the mid-1980s, MI5 estimated that eighty-five per cent of the organisation’s intelligence was the result of security force leaks. The largest single source was the Ulster Defence Regiment.

Nelson did not see himself as a terrorist at this time, however, but as an undercover soldier - and, to an extent, so too did his handlers. As one of those handlers would later comment: ‘He was a soldier not a tout. He saw himself as part of a team.’ But he was certainly being deployed to facilitate acts of terrorism.

A senior Army officer would eventually give a statement to the detectives of Stevens’ team saying that Nelson had been used by the FRU to target individuals. Through Nelson, the British Army was taking effective control of the UDA’s death squads, and directing them towards known - or suspected - members of the IRA.

Inevitably, there were mistakes. In May 1988, Nelson selected a man called Terry McDaid for execution. McDaid and his wife Maura were settling down to watch the news on television at their home in north Belfast when there was an enormous crash at the front door. ‘Terry and I just sat and stared at each other,’ Maura recalled. ‘The living room door flew back to the wall. Two men were standing at the door, they were completely clothed, there was no flesh to be seen. They ran in and just started firing.’

McDaid, twenty-nine, was shot seven times, and died within minutes. The intended target had been his older brother Declan, who lived two streets away. The FRU had been aware of the plot to murder Declan McDaid for seven months by the time Terry was shot dead. Nelson would later tell his solicitor, the police and a journalist that the FRU had provided the incorrect address, but later withdrew this claim.

By early 1989, Nelson appears to have been coming under pressure from both the UDA and his handlers at the FRU, with each organisation complaining that he was insufficiently active. By 6 February, however, his main FRU handler was noting in her contact form, with evident satisfaction: ‘Of late, Nelson has been more organised and he is currently running an operation against selected Republican personalities.’ One of these ‘personalities’ was the lawyer Pat Finucane.

Six days later, Pat Finucane was at his home in north Belfast, eating Sunday dinner with his wife Geraldine and their three children. On hearing a loud bang at the front door the couple leapt up, opened the kitchen door and looked down the hall. Striding towards them was a masked man wearing a green combat jacket that was belted at the waist. Large black gauntlets covered his forearms. He held a gun in his left hand. A second gunman was behind him.

The shooting began just as Geraldine reached out to press an alarm button. It was fast and furious at first, then slower, more deliberate. She curled up with her hands over her head, and was hit in the ankle by a ricocheting bullet.

Pat Finucane was thirty-nine. He was from a republican family: three brothers had been members of the IRA. As a solicitor, he had advised many members of the organisation, including the hunger striker Bobby Sands, and Gerry Adams. He also represented Protestants accused of terrorist offences.

Some within the British Army clearly believed Finucane to be a member of the IRA: he appeared within the records of the Northern Ireland headquarters as ‘Patrick Finucane, RC, 21 Mar 49(D) PIRA P2327’. MI5 also had little time for Finucane, and whether the agency believed him to be a terrorist or not, it wished others to believe that he was. For some time before that Sunday evening, MI5 had been spreading rumours about the lawyer. It was part of what the agency called a Counter-Action campaign that was being deployed against a number of prominent figures in the nationalist community at that time. The aim, the agency said, was to ‘unnerve’ these individuals. MI5 knew that the rumours about Finucane were reaching loyalist paramilitaries, yet it was not until after he had been shot dead that John Deverell, the head of MI5 in Northern Ireland, concluded that they had been ‘on dangerous ground’, and began to rein in the campaign. Even then, some MI5 officers wanted the Counter-Action activities to continue in order, as they put it, to ensure that ‘Republican players feel that they, too, are as exposed as the members of the security forces who live daily under threat of the assassin’s bomb or bullet’.

The RUC also believed Finucane to have been too close to the IRA. In November 1988 four senior officers, including Jack Hermon and the deputy head of Special Branch, Brian Fitzsimons, complained during a meeting in Belfast with junior Home Office minister Douglas Hogg that some lawyers in the province were ‘effectively in the pockets of terrorists’. When Hogg asked for more information, Special Branch provided him with documents identifying Finucane.

A few weeks later, Hogg told the Commons: ‘I have to state as a fact, but with great regret, that there are in Northern Ireland a number of solicitors who are unduly sympathetic to the cause of the IRA.’ Nationalist MPs were appalled, with one, Seamus Mallon, immediately predicting that ‘there are lawyers . . . who have become targets for assassins’ bullets as a result of [HOGG’S]statement’. Less than four weeks later, the two gunmen were striding down the Finucanes’ hallway, opening fire.

When the shooting stopped, Geraldine opened her eyes and saw her husband lying on his back beside her. His dining fork was still in his left hand. He had been shot six times in the head, three times in the neck and three times in the torso. One of the first detectives at the scene would later recall: ‘I had attended the scenes of some two hundred murders, suicides and sudden deaths, but what lay before me was a picture of ferocity the likes of which I had encountered few times before.’ The gunmen had downed Finucane with shots to the chest before standing over him and shooting him in the face. ‘His face was heavily covered in powder burns, which indicated that he had been shot several times at a range not greater than 15 inches.’ Finucane’s three young children had been watching.

Three inquiries would subsequently conclude that Finucane was not a member of the IRA, but a lawyer dedicated to defending his clients, who sometimes included members of the IRA. As part of the peace process, Peter Cory, a retired judge of the Canadian supreme court, was asked by the British and Irish governments to examine allegations of collusion between the security forces and paramilitaries. Cory concluded that in the case of Finucane, ‘both military and police intelligence fundamentally misconstrued the role of solicitors and failed to draw the essential distinction that exists between lawyers’ professional obligations, on the one hand, and their personal alliances, on the other’.

A subsequent review by the former war crimes prosecutor Sir Desmond de Silva QC lamented that ‘a lawyer could so callously and tragically be murdered as a result of discharging his professional legal duties’. In addition, John Stevens would conclude that Hogg had been ‘compromised’ and that his comments were unjustified.

Nelson was deeply involved in the murder of Finucane. He had passed the lawyer’s photograph and address to the UDA, and may have been watching the house shortly before the attack. Cory concluded that he had seen ‘strong evidence’ of collusive acts by the FRU, Special Branch and MI5, but that the question of the FRU’s advance knowledge of the attack could be resolved only through a public inquiry.

De Silva pointed out that during the period at which Nelson was being tasked with the targeting of members of the IRA, he was an employee of the Ministry of Defence. ‘The very nature of Nelson’s re-recruitment from Germany and his subsequent handling leads me to the conclusion that by 1989 Nelson was, to all intents and purposes, a direct State employee,’ he said. ‘The FRU must, therefore, bear a degree of responsibility for whatever targeting activity Nelson carried out in his dual role as a UDA Intelligence Officer and a FRU agent during this period.’ And while de Silva did not conclude that there had been ‘an over-arching State conspiracy to murder Patrick Finucane’, he did conclude that the lawyer would not have been murdered ‘had it not been for the different strands of involvement by elements of the State’.

Although the murder of Pat Finucane would become one of the major strands of Stevens’ investigation, his team was originally brought over from England seven months after the lawyer’s death to investigate the killing of a twenty-eight-year-old poultry processor called Loughlin Maginn.

Maginn had been mistakenly identified as a terrorist and his details placed on one of the montage cards of suspects’ photo-graphs used at security force checkpoints. In August 1989 a masked UDA gang fired several shots into his living room, then clambered through the shattered window to finish him off. Two of the UDA men had also been serving as soldiers with the Ulster Defence Regiment.

When Maginn’s family remonstrated that he had had no connection with the IRA, the UDA attempted to justify its actions by producing a twenty-minute video, shot by soldiers from the UDR, which showed the wall of a police briefing room covered with photographs of IRA suspects. Maginn was among them. There was uproar among Northern Ireland’s Catholic communities at this all too rare but irrefutable evidence of collusion between loyalist killers and the British state. An outside police investigation became unavoidable and John Stevens was appointed to run it.

Shortly after his arrival, senior military officers told Stevens that the Army never ran agents of any kind in Northern Ireland. But it wasn’t long before Stevens’ team identified Nelson as one of the Army’s key assets. It was the beginning of the end for the FRU’s operations.

It was at this point that the mysterious fire broke out at the team’s incident room, destroying their computers and in-cinerating the documents they were storing. Nelson was tipped off that he was about to be uncovered and fled to England, where arrangements were made for him to receive counter-interrogation training. He was arrested thirty-six hours later, however. The FRU immediately recovered his index cards of potential targets, which were concealed from the Stevens team for the next four months.

Ignoring the FRU’s advice, Nelson made a series of self-incriminatory statements to Stevens’ team, and even agreed to their suggestions that he write a long account of his time as a British Army undercover agent. In spite of the fire, in time, Stevens sent a file detailing Nelson’s involvement in several murders and other serious crimes to the Director of Public Prosecutions. At this point the Army and senior Ministry of Defence officials leapt into action to conceal the truth about the FRU’s involvement in the management of terrorism.

After Stevens passed his file to the DPP, an officer on the Army’s general staff sent a submission to the Defence Secretary, Tom King, which warned of the damage that could be caused should Nelson be put on trial. King recognised that Nelson was ‘a terrorist, thug and hooligan’ but also a ‘productive source’ who, he had been told, had saved lives. His initial view was that Nelson ‘should not go near the courts’. He later questioned the accuracy of some of the information he had relied on and warned that Nelson could not be protected from prosecution if he had ‘gone beyond the limit’. The general staff officer observed that although Nelson was now relying on the MoD to keep him alive - ‘either in or out of prison’ - and dependent on the department to protect the lives of his family, ‘such protection would be conditional on his remaining silent about our covert operations’. The following month, arrangements were made to pay £1,650 a month to Nelson’s wife. A few weeks later, a memo from the same staff officer to the MoD and the Army’s Northern Ireland HQ said that Nelson should be reassured that his wife was being cared for and that his family would be resettled once he was released from prison, ‘subject to his remaining silent about what he knows’.

It is far from evident that government ministers had been in control of the events that had led to the death of Pat Finucane and the many others who were targeted by Nelson. It is possible that the FRU and Special Branch were permitted to operate under a system of political oversight that was so loose that the control that the state was exerting over loyalist paramilitaries could always be disavowed.

But regardless of how long the reins may have been, by late 1990 government ministers, senior civil servants and the Army’s general staff were clearly concerned. They feared that the evidence of state-sponsored criminal violence - evidence that had been half-hidden for decades amid the confusion, the dis-trust and the daily recrimination of Northern Ireland’s bloody little war - was about to be forced into the open.

There were Cabinet-level discussions about the impending prosecution, with King and Peter Brooke, the Secretary of State for Northern Ireland, both arguing that the case should quietly be shelved, and with David Waddington, the Home Secretary, expressing concern on behalf of MI5.

By this stage the entire Cabinet must have been fully aware that their security forces had been enabling a death squad. Brooke appears to have become slightly frantic, claiming that lives could be lost if Nelson appeared in court. The Prime Minister, John Major, described himself as conflicted, but indicated that charges should be brought if there was a chance of a successful prosecution.

In Belfast, meanwhile, the Director of Public Prosecutions of the province was coming to the conclusion that it was in the public interest to bring charges. Along with the UK Attorney General, Patrick Mayhew, he withstood significant political pressure to drop the case against Nelson. Eventually, the DPP decided that there was sufficient evidence to charge Nelson with two counts of murder, four of conspiracy to murder, one of attempted murder, and a number of lesser charges.

At this point the Cabinet Secretary, Sir Robin Butler, became more engaged, sending a ‘Top Secret’ minute to Major in which he highlighted the public interest risks in taking Nelson to trial and attempted to persuade the Prime Minister to take steps to oppose it. Not long afterwards, Major’s principal private secretary was noting that the collapse of the prosecution would be ‘a very good outcome’, which appears to have reflected the prevalent view at the highest levels of government.

By the time Nelson finally came to trial in January 1992, the murder charges had, without explanation, been dropped. Instead he was permitted to plead guilty to five charges of conspiracy to murder, and was sentenced to ten years’ imprisonment. Previously, the DPP had appeared adamant that there should be no suggestion that he had accepted a plea bargain. It subsequently emerged, however, that the DPP had told the Attorney General that he was obliged to consider any approach by the defence, and that such an approach had been made.

As a consequence, Brian Nelson, Agent 6137, was not cross-examined. Any light that he could have shed upon the role that the British state had played in the murder of its own citizens was quietly snuffed out.

Nelson served a little more than four years before being released. The Army was as good as its word - he had maintained his silence, after all - and he was given a new identity and a new life. His by-now-estranged wife and their children were provided with a new home in the north of England.

In April 2003 the MoD issued a brief statement announcing that Nelson had died of a brain haemorrhage, aged fifty-five. Journalists were briefed that he had been living in Canada. In fact, he had been living in Cardiff, under the name Brian Thompson. His death certificate listed his occupation as ‘Army Officer (Retired)’. Two weeks later, after more than thirteen years investigating collusion between the British state and the terrorists it was supposed to be combating, Stevens’ third and final report was completed. By then, his work had led to the conviction of ninety-four people. None of them were from the Army’s FRU, Special Branch or MI5. Instead, the FRU’s commanding officer had been promoted, and Nelson’s main handler had been promoted and decorated.

In the course of their investigation, Stevens’ team had taken 9,256 statements and gathered 10,391 documents, totalling more than a million pages, not counting those lost in the fire at Seapark in Carrickfergus. His final report ran to several thousand pages. Just nineteen of those pages were made public.

It would be another nine years before the full extent of the British state’s involvement in the murder of Pat Finucane would emerge. In 2012, de Silva’s review of the case found that it went far beyond the control, through the Army, of the man who was feeding the names and locations of potential targets to the UDA’s death squads.

Police officers had been urging loyalists to kill Finucane, while holding them for questioning about other offences. The man who supplied the weapons used to kill Finucane had been a Special Branch informant for the previous eighteen months. He had warned his handlers that an attack was about to take place, but they took no action. The man who drove the getaway car later confessed to police, at which point he too was recruited as an agent and, in accordance with the provisions of the Walker Report, the case against him was dropped.

Nelson was the most notorious of the British agents operating within the loyalist paramilitaries’ ranks, but he was far from alone. Long after his investigations into collusion in Northern Ireland were wound up, Stevens disclosed that of the 210 people his team arrested, only three were not agents of the British state. Some were working simultaneously for the police, the Army, MI5 and, he hinted, MI6. They were making handsome sums of money, frequently while fighting against each other, ‘which was all against the public interest and creating mayhem in Northern Ireland’.

As the truth about collusion and agent-running operations seeped slowly into the open, elements of the security forces could be seen to have been embroiled in one cold-blooded murder after another. The official narrative - that the police and Army were attempting merely to defeat terrorism, within the law - appeared increasingly threadbare. But attempts to discover what actually happened have struggled and frequently failed.

The British government has refused to convene any further public inquiries into specific events, blaming the length and cost of the thirteen-year inquiry into the fatal shootings of fourteen civilians by the Army on Bloody Sunday. David Cameron admitted that there were ‘frankly shocking levels of state collusion’ in the murder of Pat Finucane, and one of his advisors told the Cabinet Secretary that the Prime Minister ‘shares the view that this is an awful case, and as bad as it gets: far worse than any post 9/11 allegation’.

Nevertheless, Cameron’s government reneged on a supposedly binding international agreement to hold a public inquiry. Meeting Geraldine Finucane at Downing Street to explain his decision, Cameron raised one finger in the air, according to a number of those present, drew a circle, and said that there were ‘people in buildings all around here who won’t let it happen’.

Other mechanisms for establishing the truths about deaths - such as inquests, litigation, Police Ombudsman’s inquiries or detectives’ cold case reviews - have proved largely ineffective for an assortment of reasons.

The coronial inquest system, which has been recovering the truth about sudden or unnatural deaths in England and Wales for 800 years, appeared in Northern Ireland during the Troubles to have bowed to the more pressing requirements of a counter-terrorism campaign. Coroners were unable in law to record unlawful killing verdicts, and were reluctant at times to probe too deeply into possible criminal conduct on the part of the security forces.

Since the conflict came largely to an end, the inquest system appears to have been unable to reassert its independence: it is not unusual to see inquests suffer one delay after another as a consequence of the failure of the police or Ministry of Defence to produce relevant files. And these delays are measured not in months, or even years, but in decades.

As of 2014, inquests had yet to be concluded into seventy-four killings during the conflict in Northern Ireland. Around half were inquests that the Attorney General had ordered to be reopened after finding that the original hearings were flawed; half were cases that had been adjourned shortly after the death, and never completed.

By April that year, the average time that families had been waiting for an adjourned inquest to be concluded was twenty years and seven months. Almost all concerned killings by police officers or soldiers, or by loyalist paramilitaries who were suspected of being state agents.

The Historical Enquiries Team (HET), the police unit set up in 2005 to re-examine unsolved murders, knew nothing about the two vast warehouses of documents that the MoD maintained at Swadlincote in Derbyshire, and nobody at the MoD saw fit to inform the team of their existence. When this archive was reported in the media, a senior HET investigator said: ‘There could potentially be documentation about every case we are interested in.’

The HET was already facing questions about its independence after it had emerged that former Special Branch officers were among the gatekeepers who were deciding what intelligence material held in Northern Ireland it would be permitted to see. The HET unit was shut down after a highly critical report by Her Majesty’s Inspectorate of Constabulary concluded that it was investigating killings by soldiers and police with less rigour than it was investigating killings by paramilitaries.

At the time of writing, the Police Ombudsman for Northern Ireland was attempting to investigate around 300 allegations of serious wrongdoing by officers during the Troubles, including collusion in murder. These included the Glenanne gang killings, and the question of whether police failed to prevent Stakeknife’s killings. As a consequence of budget cuts, the Ombudsman has warned that some investigations will take twelve years to complete.

Like the coroners and the HET, the Ombudsman’s investigators have experienced enormous difficulty in accessing the intelligence documents that they need to complete their inquiries. In 2014 the Ombudsman was compelled to bring judicial review proceedings against the Chief Constable over his refusal to hand over papers concerning the role of agents of the state in around sixty murders, including that of a police officer who was killed in 1992.

Official documents, of course, can provide a key to understanding the official mind. As a consequence, in Northern Ireland not all have survived. Many were destroyed the moment they were no longer required, as stipulated by the Walker Report. Others vanished as peace began to be established. Like those colonial officials who lit the global end-of-Empire conflagration that became known as Operation Legacy, some senior RUC officers saw little reason to risk the eventual disclosure of their most sensitive records.

In 2011, police admitted that files that had been held at Gough Barracks, their regional headquarters in County Armagh, had been destroyed within weeks of the 1998 Good Friday Agreement. The papers included incident reports dating back to the 1970s and notes of interviews of murder suspects who had been questioned at the barracks between 1985 and 1993. This was a period when there is alleged to have been collusion between a number of police officers and loyalist gunmen who were killing local Catholics.

The destruction operation was made public only after the family of a young Catholic man shot dead by loyalists in 1991 discovered that none of the police records relating to his un-solved murder any longer existed. The reason given for their destruction was identical to that given by the Ministry of Defence for the non-disclosure of some of its most sensitive papers - they had been stored in an area where asbestos had been found.

What the announcement did not mention is that contractors brought in to deal with the asbestos problem had warned that it would be unsafe to burn or shred the documents, and suggested that they should be dumped either in a landfill site or at sea. One particular minute, echoing the dumping of the most damning documentation of Kenya’s brutal conflict into the ‘very deep and current free waters’ of the Indian Ocean, recorded that a senior officer said he favoured dumping the papers in Beaufort’s Dyke, a deep underwater trench between Northern Ireland and Scotland. The officer explained that this would be an advisable course of action because ‘the action of the sea water on the paper would over time pulp it and destroy the information held thereon’. He eventually decided on cost grounds that they should be buried in a landfill site.

Despite the warnings they had received, senior RUC officers ruled that the papers should be shredded before being secretly removed to the landfill site. Much to the alarm of the contractor carrying out the work, a police officer was stationed inside the room to watch the shredding being completed. So concerned was the contractor that he contacted the Police Authority, re-quest-ing indemnity against legal action should the officer become contaminated.

Today, the shredded remains of the Gough Barracks archives, and the secrets that they held, are buried fifteen metres beneath an old landfill site in north Belfast that is due to be turned into a park.

By the time Stevens’ three inquiries in Northern Ireland came to a conclusion in 2003, the documents that his team had amassed were estimated to weigh around 100 tonnes. Following the fire at his incident room, he had been taking very good care of them: before he left Belfast they were loaded into Ford Transit vans and driven to an airport where a Hercules transport aircraft was waiting. The vans drove straight up a ramp and into the aircraft, which took off immediately for a secure location in England.

In 2007, members of the Stevens’ team complained that the MoD and MI5 were pressing Scotland Yard for the return of the documents. ‘There are calls from certain agencies for their documents to be returned,’ said one officer. ‘In some cases we have handed them back and they have been shredded. The pressure on us is growing and it has got to the stage where we have told them what part of the word “no” don’t you understand?’

In 2011, the Stevens archive was handed to the police in Northern Ireland, although Scotland Yard says it kept a copy in electronic format. Three years later, this author asked the Yard whether it considered this copy of the archive to be subject to the provisions of the Public Records Acts, to be preserved and handed eventually to the National Archives at Kew. The Yard spent two months contemplating whether the Freedom of Information Act gave it a reason to not answer the question. Eventually, the Yard said that it did not believe this copy was subject to the Public Records Act, but that it was ‘likely to be considered for permanent preservation’.

So it was likely that the archive wouldn’t be destroyed, but there was no guarantee.

The copies of the Stevens papers that were handed over to the police in Northern Ireland were sent to an equally secure location: Seapark, the high-security police facility at Carrick-fergus where the Army’s arsonists staged their desperate attempt to bring Stevens’ inquiries to a halt in January 1990. They sit there today, unreachable, alongside the documents that the coroners have been unable to get their hands on, and the files the Police Ombudsman was permitted to read only once he had won a courtroom battle with the Chief Constable. Nearby are stored the secret reports written by two other English detectives, John Stalker and Colin Sampson, after they were drafted in to investigate the RUC’s so-called shoot-to-kill policy of the early 1980s. Doubtless there are also police files on acts of collusion by soldiers of the Ulster Defence Regiment, and on the murderous activities of the MRF. All these papers, and many others, are held together: the annals of the dirty war that the United King-dom fought within its own borders for more than thirty years.

The gatekeepers to the archive at Seapark - the men and women who decide what is made public, what is redacted, what is withheld - are the officers of the ‘Legacy Support Unit’ of the Police Service of Northern Ireland. Many of them are former Special Branch detectives, brought out of retirement specifically to perform this task.

In 2015, George Hamilton, the Chief Constable of Northern Ireland, used the term ‘The Vault’ to describe this archive while giving a television interview. ‘It’s a colourful metaphor - “Vault” - but let’s use that,’ he said. ‘If The Vault was to be opened, I know there will be literally millions of documents. I’m not just talking about intelligence documents, I’m talking about plans for covert operations, I’m talking about minutes of meetings.

‘My understanding is that the IRA, the UVF and the other players in this didn’t keep notes or minutes of meetings or records of decisions. We did. And I think all of that has left us somewhat exposed.’

Police records in the UK are subject to the Freedom of Information Act, but they are not subject to the Public Records Acts, or to the Thirty-Year Rule - soon to become a Twenty-Year-rule - of those Acts.

There’s another reason why the Vault may remain locked for ever, however. Hamilton made it clear that his repository contained papers that would be enormously troublesome for people other than police and intelligence officers, civil servants and ministers. ‘Other people have stories to tell and questions to answer,’ he said. When the door to The Vault is opened up, there should be no doubt that ‘out of that will pour material that will present challenges for other people in the system’.

The implication was that the Vault contains material that all sides engaged in the conflict would wish to remain buried, and for a very long time. Furthermore, while many of those who waged that war have since passed away, others are now in govern-ment, in both Westminster and Stormont.

‘If we’re sitting on millions of pages of intelligence documents from a very busy time, when there were killings happening almost on a daily basis, and some sort of atrocity happening on a regular basis, you would expect that there will be material there that will present challenges for individuals,’ Hamilton said. It would also, he made clear, provide opportunities for investigators.

‘That’s the way it works.’

This is an edited extract from The History Thieves: Secrets, Lies and the Shaping of a Modern Nation by Ian Cobain (Portobello Books, £20), which will be reviewed in The Irish Times next month by Chris Mullin