The break-in at the Castlereagh police base in east Belfast was a major embarrassment for police and put the developing peace process in Northern Ireland under severe pressure at the time.

That someone could waltz into what was supposed to be one of the most secure police stations on the planet and make off with hugely sensitive files stunned security analysts, who immediately speculated on it being an inside job.

Coming three weeks before the IRA put the second trance of its arsenal of weapons "beyond use" and with the political peace at Stormont uneasy, it was the last thing the Government wanted.

It was a Sunday evening, March 17 2002 - St Patrick's Day - when Special Branch secrets were removed from an office - room 2-20 - in the complex where top terrorist suspects were interrogated down the decades.

The room contained A-Z files on Special Branch officers, their phone numbers, code names of their agents and their handlers.

As always the office was manned. The officer on duty, a Special Branch detective constable, was assaulted, tied up and had his mouth and eyes taped up by three men who suddenly entered the office and then made off with the masses of sensitive information.

In the months that followed more than 100 Special Branch officers had to move home and others had to fortify their properties.

Hundreds of police officers were put to work investigating the robbery. Initially the then Chief Constable Sir Ronnie Flanagan - a former Special branch chief - said he would be "most surprised" if paramilitaries were responsible.

But before the end of March 2002 police said the investigations led them most strongly towards believing the IRA was behind the break-in.

The IRA insisted it was not involved and blamed elements of British intelligence. A review later carried out by Sir John Chilcott - the man now heading the Government's inquiry into the Iraq War - later concluded there was no evidence of involvement by the intelligence services.

However, six months after the break-in Larry Zaitschek was firmly in the PSNI cross-hairs.

The American had been a chef in Castlereagh and was interviewed twice by police before returning home soon afterwards.

A few months later, after a detailed investigation of his activities, finances, travel and examination of the people he associated with in Belfast, detectives decided he was their man and prepared the extradition case which was finally abandoned today.

One of those he was associated with was Denis Donaldson, the key administrator in the Sinn Fein offices at Stormont after devolution.

In October 2002, police raided the Sinn Fein offices and unmasked what was claimed to be a republican spy ring at the heart of government.

What became known as Stormontgate led to the suspension of devolution and the reintroduction of direct rule when the then First Minister David Trimble threatened to collapse the administration.

Donaldson was arrested and remanded in custody charged with having documents likely to be of use to terrorists.

However in 2005 prosecutors said they were dropping the charges citing "the public interest".

That public interest became clear days later when in a scene straight out of a spy novel, Donaldson admitted being a British agent in the heart of the republican movement.

He made a public statement admitting he had been a British agent at the time of the Stormontgate raids and the Castlereagh break-in.

He said he had worked for British intelligence and Special Branch since being recruited in the 1980s after "compromising myself at a vulnerable time in my life".

Donaldson was expelled by a stunned Sinn Fein and disappeared from Belfast.

In December 2005 he was tracked down and interviewed by a Sunday newspaper journalist who found him living in a run-down cottage across the border in Co Donegal.

In March 2006 he was shot dead outside the cottage. The IRA, which was on ceasefire, was suspected of being responsible - despite its repeated denials.

This year however the dissident Real IRA claimed responsibility for murdering Donaldson in an interview with another Sunday newspaper journalist who received their claim of responsibility for the murders of Sappers Mark Quinsey, 23, from Birmingham, and Patrick Azimkar, 21, from London, who were shot dead outside Massereene Barracks in Antrim in March.

The PSNI took Suzanne Breen to court seeking notes and telephone records of her interview, but last month a Belfast judge ruled she need not hand them over.

Recorder Tom Burgess said her right to life - she said she had been warned she would be under sentence of death by the Real IRA if she revealed her sources - outweighed any other public interest.

As it stands there will be no prosecution over Castlereagh, no prosecution over Stormontgate, and so far, no prosecution in the Irish Republic over the murder of Denis Donaldson.