The raid on Special Branch offices in Belfast was described by the Government as "a breach of national security" and authorities believe it may be one of the most serious intelligence scandals to emerge during the Troubles.
The lives of security force informants may have been endangered by the theft at the weekend of sensitive documents from an office used as a call centre for those contacting Special Branch.
Almost all the facts point away from paramilitary responsibility and towards intelligence personnel. One source familiar with the investigation said the break-in had been carried out "in a true professional and slick way, by people who knew what they were doing".
It is already acknowledged at a high level that the incident represents an unmistakable sign that something is rotten in the intelligence underworld.
A source said: "It's not the first time strange things have happened. There has to be a cleaning out of the stables – which won't be an easy process but it has to be done."
In addition to the police investigation into the incident, John Reid, the Secretary of State for Northern Ireland, announced yesterday that a review would be carried out by a "distinguished" figure. He declared: "I am absolutely determined to establish where the truth lies in this matter. This independent review will proceed in parallel with the criminal investigation and will therefore start straight away. It will report directly to me."
Police sources suggested that the purpose of the raiders might have been to embarrass the Special Branch, or to gather material for blackmail or ransom, or to collect information which they might threaten to release if they are charged in connection with some other misbehaviour.
In political circles, however, there is a suspicion that deeper problems may exist with intelligence. There is talk of "rogue elements" who may be at work within the Special Branch or other intelligence organisations.
One theory yesterday was that some of the hundreds of officers who have left the police force in the wake of the paramilitary ceasefires may have been involved.Reuse content