New details about collusion between the RUC and the loyalist killers who targeted the 38-year-old 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.
The report 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.
Mr Finucane’s son Michael said he is not surprised by the revelations.
“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,” he said.
Four chapters of a report by John Stevens were published in 2003.
In the released nine-page chapter six, entitled Murder Investigation, Mr Stevens criticised the handling of the murder weapon by the RUC.
He wrote: “This was not a case of administrative oversight, or even some loss occasioned by a lack of care. I believe it was a clear and deliberate decision to relinquish control of a key exhibit, resulting in the destruction of vital evidence.
“The lack of records has prevented the identification of the person responsible for this decision. The potential consequences of this particular disposal are obvious, with allegations made from the start of collusion between the security forces and loyalist paramilitaries.
“The face that the firearm, when recovered, was found to have originated from the army no doubt fuelled that suspicion.”
He said the decision not only compromised a key exhibit, but also put any solider using it legally at risk of being implicated.
Chapter six was released following a four-year battle by RTÉ reporter Richard Dowling under the UK’s Freedom of Information Act.
Its contents emerged as a mural to commemorate the continuing legacy of Mr Finucane was unveiled close to where he grew up in west Belfast and days before a new report into his death is published.
His widow Geraldine has vowed to keep up a campaign for a full public inquiry, regardless of the findings of the review, being carried out by Desmond de Silva.
The Catholic father- of-three was shot dead when UDA/UFF gunmen used sledgehammers to burst in through the front door of his home in north Belfast in Feb 1989.
Chapter six also examined the RUC’s handling of the investigation into Brian Adam Lambert, a Protestant killed by loyalists who mistook him for a Catholic.