The Chief Constable of the Police Service of Northern Ireland has effectively admitted the break-in and theft of documents from Special Branch offices in Belfast was an inside job.
Sir Ronnie Flanagan said he would be "most surprised" if paramilitaries or civilians were responsible. However, he considered it "impossible" that the incident had been given official sanction by any military or intelligence agency.
The PSNI yesterday declined to comment on reports that the CCTV system at the Castlereagh base was not connected to video recording equipment. A spokeswoman said it would be "inappropriate" to comment ahead of the completion of the police criminal investigation or the review ordered by the Northern Secretary, Dr John Reid. The PSNI also declined to comment on claims that police believe it was carried out by three members of British military intelligence.
In an interview with Sunday Life, Sir Ronnie, who retires this weekend, said he did not believe the incident was an officially sanctioned intelligence operation.
"It is an aggravated burglary of the most serious nature so I can't contemplate that this would have been sanctioned at any level by anyone in an official position. This is such a serious criminal act that anyone involved would be guilty of equally serious offences as those who carried it out."
Sir Ronnie claimed the office raided contained limited information which increased the mystery. "If you knew no more than that this was a Special Branch base and believed that this office was the hub of that base, you might have expected that there would be much more stored there. There isn't, and this is the conundrum."
The Chief Constable said the investigation was difficult because there were so many lines of inquiry. He had received calls from people concerned for their security and worried that their identities could be compromised.
The Sinn Féin president, Mr Gerry Adams, will discuss the break-in with the British Prime Minister, Mr Tony Blair, at Downing Street today.
Meanwhile, the British government's appointment of Sir John Chilcott to lead the review into the Castlereagh incident has been criticised by members of the Policing Board. The board's deputy chairman, Mr Dennis Bradley, questioned whether Sir John's links to the intelligence services provided the right image of independence.