By Dominic Casciani
BBC News Online
The unmasking of a top-level mole in the IRA - named as Freddie Scappaticci - has peeled back another layer of Northern Ireland's secret war. But will we ever know the full extent of what took place in the shadows?
Francisco Notarantonio: Allegedly set-up by rogue agents
On 9 October 1987, pensioner Francisco Notarantonio was asleep at his home in west Belfast.
As he lay in bed, loyalist gunmen burst into the home and shot him dead in front of his family.
They appeared to be acting in the belief that Mr Notarantonio, a republican sympathiser and old friend of Sinn Fein leader Gerry Adam's father, was a top IRA figure.
He had indeed been in the IRA - the completely different one of the 1940s. For decades, Mr Notarantonio had been nothing more than a taxi driver and grandfather.
Like the later killing of Belfast solicitor Pat Finucane, it became almost an article of faith for many in nationalist areas of Belfast that the secret hand of military intelligence directed the killing for its own ends.
The Notarantonio murder was more than just a tragedy for his family.
However, what made the Notarantonio case unique was the suggestion that he was killed to protect a top-level IRA mole codenamed "Stakeknife".
Today, we know that Stakeknife did indeed operate within the higher echelons of the IRA - a revelation that completely changes our understanding of the secret intelligence war.
Since 1989 there have been three huge inquiries, all led by the Metropolitan Police Commissioner Sir John Stevens, into how the security services recruited and ran paramilitary agents in Northern Ireland.
His latest and most damning report concluded there had been collusion between elements of military intelligence, members of the police and loyalist paramilitaries in the murder of Mr Finucane and another man, Adam Lambert.
Thousands of documents
'Collusion' took place
More revelations expected
In many respects, the basic facts behind the inquiries were never in doubt - that the security forces had long sought to recruit and run agents within paramilitary organisations.
But the question for Stevens has long been whether those running agents went beyond the law and allowed or even condoned the killing of people they were meant to protect.
Over the past three decades there are untold examples of suspected informants on both sides being kidnapped, tortured and killed by paramilitaries.
The IRA went as far as setting up its own internal security unit - supposedly headed by the man now exposed as Stakeknife.
While Stevens has peeled back many of the layers of military intelligence's involvement in loyalist groups - very little is known of its infiltration of the IRA.
The full story of Stakeknife, a story republicans will not necessarily want told, may turn out to be far more sinister than anything that has gone before it.
For if military intelligence had indeed run an agent high up in the IRA in the 1980s, how much did it know about the IRA's plans and activities?
Intelligence man speaks out
Reports of a top-level IRA mole first emerged in the wake of Mr Notarantonio's killing.
The allegations gathered momentum when a former member of the Force Research Unit began talking to the media.
Martin Ingram (not his real name) claimed FRU agent runners had fed false information about Mr Notarantonio to loyalist gunmen.
Martin McGartland: Survived gun attack
Says he was not properly protected
Others also speaking out
They did this, he said, because they knew the Ulster Defence was going to try and assassinate Stakeknife.
Since then, the British Government has sought gagging orders against a number of newspapers which have attempted to publish more of Ingram's allegations.
But Martin Ingram is not the only agent to have come forward.
In the five years since the signing of the Good Friday Agreement, more and more men who say they were recruited to infiltrate paramilitaries have spoken out.
Many of these men say their lives are in danger because they are not being properly protected.
One former IRA agent, Martin McGartland, narrowly avoided assassination when what is believed to be an IRA gunman tracked him down in 1999.
Mr McGartland has bitterly complained that his former handlers have hung him and others out to dry. He wants the full story of how military intelligence operate to be known.
For his part, Martin Ingram recently predicted a public inquiry into the murder of Pat Finucane will ultimately only serve military intelligence's interests as it would prevent the full story of an undeclared and legally ambiguous "dirty war" from ever being known.
More to come?
But what is also clear is that Northern Ireland is nowhere near to holding some kind of South African-style truth and reconciliation commission at which people would be prepared to openly talk.
Instead, the stories of agents are increasingly emerging like pieces of an enormous jigsaw.
Some of them are coming out through the Bloody Sunday Inquiry, others through the media.
But while there may be an enormous public interest in this shadow world, there are plenty of people inside the security forces and both loyalist and republican paramilitary groups who would prefer these people not to talk.