Investigation will expose Britain's role in 'Dirty War'
It's a decision no-one could have ever foreseen, the British investigating 'their own' for crimes committed in the Troubles.
But that is what will happen now after the North's DPP Barra McGrory made an astonishing announcement in Belfast yesterday.
Freddie Scappaticci was Britain's most prized asset inside the IRA and, until he was unmasked as the agent 'Stakeknife' in 2003, he was also their most secret weapon against the Provisional IRA He denies the claims that he is 'Stakeknife'.
The problem for the British, however, is that the man known as 'Scap' was also alleged to be a serial killer.
He was second-in-command of the Provo internal security unit, known by IRA members as 'The Nutting Squad'.
Mr McGrory has been given a dossier by the Police Ombudsman for Northern Ireland linking Scappaticci to 24 murders. Some of those victims were doing exactly what Scappaticci, from the Ormeau Road in south Belfast, was doing - passing on IRA secrets to British Intelligence.
In Scap's case it was to the shadowy British Army outfit known as the Force Research Unit (FRU).
From the 1980s and into the early 1990s, military intelligence could not have picked a better position to infiltrate. The IRA was made of up a series of Active Service Units (ASU), small groups of members who operated almost autonomously from the IRA's Northern Command, which covered 11 counties.
These units were designed to thwart RUC investigations into IRA activities; if one group was closed down via arrests and imprisonment, it didn't affect other ASUs.
But the IRA had one critical weakness - and the FRU exploited it.
The Nutting Squad had access to almost all operating IRA members. With Scappaticci inside the unit, then so did the British.
A police investigation into Scap could add a damning new chapter to Britain's role in the so-called 'Dirty War'.
The FRU have been here before. Their agent inside the UDA, Brian Nelson, documented his role in setting up sectarian murders of Catholics to the Stevens Inquiry in the early 1990s.
He pleaded guilty to murder conspiracies so details of his true role remained secret. Victims included the solicitor Pat Finucane.