A gun used in the murder of a Catholic couple, which police reported they had seized, actually remained in the hands of the UVF and was used to kill pensioner Roseann Mallon.
The startling revelation will be made this week at the inquest in Belfast coroner's court into the 1994 murder of the 76-year-old in Dungannon, Co Tyrone.
Allegations of collusion surround the UVF killing of Miss Mallon who was shot dead watching television. Her family had previously been told the Czech assault rifle that killed her was a "clean" weapon.
But Sunday Life can reveal that a new forensics report on the gun by the Historical Enquiries Team (HET) shows it was used in many loyalist murders including that of Charlie and Tess Fox in Moy, Co Tyrone, two years earlier.
And the Fox family have been told that the gun, which the RUC recorded was used in their parents' killing, wasn't in fact the murder weapon.
"This is more than incompetence, it's a cover-up," said Anthony Fox. "We believe the police never properly investigated our parents' murder. After they left, we found two bullets still lodged in the walls they hadn't taken away for examination. Now we hear they got the gun wrong."
Charlie Fox, 65, and his wife Tess, 53, were shot dead in their home in September 1992. They had no political involvement but their son Patrick had been jailed for possessing an IRA bomb a week earlier.
The couple were preparing for bed when the UVF gang struck. Charlie was shot in his pyjamas. Tess took a sweeping brush to the gunman but he broke her jaw before shooting her.
They were found by their daughters in the blood-drenched kitchen. Fr Denis Faul described them as "decent, innocent people".
In a HET report last year, the family were told police had seized the murder weapon eight months after their parents' killing.
The report stated: "The vz 58 assault rifle used to kill Charlie and Tess was recovered at Kilmore in Loughall on May 10 1993. The weapon remains in the forensic laboratory."
But last week at a HET meeting the Foxes were told that, contrary to RUC reports, it had now been established this wasn't the murder weapon and the rifle which killed their parents was later used to shoot Roseann Mallon in May 1994.
Their solicitor, Kevin Winters, said: "It is deeply disturbing that the HET were misled by the original RUC material. We must probe why such erroneous information was supplied. I am raising this issue urgently with the Police Ombudsman."
One loyalist was convicted of the Foxes murder but the family say he was only "a bit player". They believe the alleged gunman, who lives in Portadown and is a born-again Christian, was never charged because he was a Special Branch agent.
Mr Winters revealed that other bereaved families are now questioning the accuracy of RUC reports about weapons used in their relatives' killings.
He said doubts had been raised about the police account of the guns involved in the 1991 loyalist triple murder at a mobile shop in Craigavon. Eileen Duffy,16, Katrina Rennie,19, and Brian Frizzell, 29, were shot dead by the UVF's Mid-Ulster brigade.
