David Gilroy was jailed for 18 years for the death of former lover Suzanne Pilley whose body has never been recovered.
However, the family of Gilroy say that if plans to destroy the evidence linked to his crime go ahead, they will never be able to prove his innocence.
The Crown Office and Procurator Fiscal Service (COPFS) has announced plans to destroy the evidence used against him.
However, the family have criticised the decision.
His stepmother Linda Gilroy told the Herald: “To get rid of evidence at this stage denies David the chance to commission experts to show how badly some of the key evidence used to convict him is wrong.
“Scotland seems to be out of line with England and Wales and other modern jurisdictions in getting rid of evidence at such an early point in a sentence,” she added.
“How many other Scottish prisoners have been, or will be, robbed of the chance to prove that they have been wrongfully convicted?”
When sentenced in 2012, Lord Bracadale spoke of the “quite chilling calmness” with which Gilroy set about disposing of the body.
Gilroy now hopes to seek expert opinions on key evidence in the case. But his supporters fear the COPFS action will destroy vital evidence denying him the chance to prove he is not guilty of the murder.
Speaking on the decision, the agency said: “Given that there are now no further appeal proceedings ongoing, the Crown has authorised the release of all productions.”
Euan McIlvride, of the Glasgow-based Miscarriage of Justice Organisation (MOJO) Scotland said “If you look at some of the high profile examples where convictions have been overturned – such as TC Campbell, Joseph Steele and Paddy Hill – they all took more than one appeal.
“For the Crown Office to take the view that it is one strike and you are out is harsh. It is entirely wrong that they are able to deny access to justice to the very people they prosecuted.”
A spokesman for the Scottish Criminal Cases Review Commission said “We reviewed Mr Gilroy’s case and concluded there was no reason to believe there to have been a miscarriage of justice.”
A spokeswoman for COPFS said that while the law states evidence must be retained until a convict is released from custody in England and Wales, there is no such law in Scotland. “David Gilroy was convicted of murder and his appeal and application to the Scottish Criminal Cases Review Commission were unsuccessful. As such there is no legal basis for COPFS to retain the productions relating to this case,” she said.