The link turned up in the only surviving prison security file on any of the three INLA men who murdered Wright - but police say they can find no records connecting the RUC agent with the gun.

They also say the agent, who was suspected of smuggling a gun to Wright killer Christopher 'Crip' McWilliams, is now dead.

The shock disclosure was made yesterday in a detailed 75-page statement on missing evidence that was issued by the Billy Wright Inquiry, which is investigating whether state agencies colluded with the killers.

The statement gave details of key intelligence that the PSNI has been unable to provide about the murder in the Maze Prison in 1997. The inquiry indicated that material provided by other intelligence agencies suggests the PSNI documents should exist.

In their statement, the inquiry panel said the PSNI has "suggested a number of reasons for any information gap that exists", but said those reasons "are not necessarily accepted by us."

But the PSNI insisted they have put a "huge amount of effort and resources" into helping the inquiry.

The special statement was issued after continuing problems with missing or destroyed evidence.

The inquiry panel has previously said that they have had problems obtaining material from every security agency connected with Wright's death.

The Prison Service was particularly criticised for losing or destroying thousands of documents, including security files from the Maze.

The link between 'Crip' McWilliams, the unnamed Special Branch agent and the smuggled gun turned up in the only security file to survive the Prison Service's destruction - one accidentally discovered by the Wright Inquiry team among other material.

The file on killer John Glennon included "a handwritten entry to the effect that a gun had previously been smuggled into prison for Christoper McWilliams by an ex-Maghaberry prisoner."

McWilliams managed to get guns inside prison twice within eight months - the first time to take a prison officer hostage in Maghaberry and then to murder Wright in the Maze.

The statement adds: "The ex-prisoner was, at the time of the hostage incident and the time of Billy Wright's murder, a RUC SB (Special Branch) informant."

But the inquiry says the PSNI say they can find no records connecting the man - who they say is now dead - to the smuggling incident.

Also missing are records of police surveillance of the top INLA leaders who plotted Wright's murder, and RUC risk assessments on Wright in the weeks before he was gunned down.

The Inquiry says other intelligence is missing on the decision to transfer Wright to the Maze from Maghaberry, the subsequent transfers of Wright's killers to the same H Block, the INLA threat against Wright and his murder.

The statement also reveals that records of payments to RUC agents have been destroyed.

At a brief public hearing in Banbridge yesterday, inquiry chairman Lord MacLean said the statement on the PSNI failures contained "no direct or overt criticism" of the service.

But the statement does say the supply of information on Special Branch agents went "badly awry"

It said "completely wrong or inaccurate information had been supplied to the inquiry" by the PSNI.

Lord MacLean said the PSNI would have the opportunity to respond during the course of evidence, which resumes next week.

A PSNI spokesman said police "are currently examining the document published today.

"We are committed to co-operating fully with the inquiry. We have conducted exhaustive searches to deliver material to the inquiry. A huge amount of effort and resources continue to be dedicated to servicing this inquiry."