The Police Ombudsman is investigating claims the 2002 burglary of Castlereagh police station was "allowed to happen to protect an IRA informer".
Intruders broke into a Special Branch office at the police base on St Patrick's Day 2002.
They escaped with sensitive files which related to officers and their agents inside paramilitary organisations on both sides.
It was one of the most embarrassing episodes in the PSNI's history.
Millions of pounds were spent rehousing officers and others whose security was compromised by the stolen information.
The BBC's Stephen Nolan Show revealed this morning that the Police Ombudsman was investigating a claim by a former police officer.
Journalist Brian Rowan said the claims were made by a former Special Branch officer.
That officer claims the break-in was allowed to happen to protect a high-level agent within the IRA.
The Police Ombudsman said: "We can confirm that we have received a referral from the Chief Constable relating to an allegation from a former police officer that the break-in at the Castlereagh Police Station was allowed to take place.
"We have written to the solicitors concerned to ask if their client is willing to assist in our investigation and are currently awaiting a response."
The PSNI said it would be "inappropriate to comment" as an investigation was taking place.