A pistol used in the murder of Belfast solicitor Pat Finucane was handed back to the British Army by the RUC, previously unpublished papers show.

New details about collusion between the RUC -- since reformed and renamed the Police Service of Northern Ireland (PSNI) -- and the Loyalist killers who targeted the 38-year-old solicitor in 1989 have been revealed in a report.

The unseen chapter from the Stevens Inquiry is highly critical of the RUC’s “inadequate” investigation in the case and found officers deliberately destroyed vital evidence, while exhibits and records could not be found and fingerprints at the scene were not compared against suspects.

It stated one of two murder weapons, a Browning pistol, was recovered by police but then given back to the British army, from where it had previously been stolen by loyalists.

In the newly-released nine-page chapter six, entitled Murder Investigation, Sir John Stevens, who led the inquiry, criticized the handling of the murder weapon by the RUC.

“This was not a case of administrative oversight, or even some loss occasioned by a lack of care,” he wrote.

“I believe it was a clear and deliberate decision to relinquish control of a key exhibit, resulting in the destruction of vital evidence.”

The previously unseen document was released following a four-year battle by RTE reporter Richard Dowling under the Freedom of Information Act in the U.K.   

Finucane’s son Michael said he is not surprised by the revelations.

He said, “Unfortunately, many other families are in a similar position to ourselves where they are finding out after the fact because the material has been held back for so long, that what they were told was a diligent and efficient and effective investigation was in fact anything but.” The contents of the secret chapter emerged just days before a new report by Sir Desmond de Silva into Finucane’s death is released on Wednesday, December 12.

A formal statement will be made to the House of Commons by British Prime Minister David Cameron. The Finucane family will travel to London to receive the report and read its contents.

They are still campaigning for a full public inquiry into his death.  His widow Geraldine has vowed to keep up a campaign for a full public inquiry regardless of the findings of the de Silva review.

Finucane, a Catholic father of three, was shot dead when Loyalist UDA/UFF gunmen used sledgehammers to burst in through the front door of his home in north Belfast in February 1989.