The prosecutor at the trial of a man convicted of murdering his wife later admitted he would have "fainted" had he been told of key evidence that has now become available, appeal judges heard yesterday.

Lord Turnbull, who was then advocate depute Alan Turnbull, also said he would have deserted the trial of Nat Fraser for further investigation.

The revelation came during the first day of Fraser's appeal against the majority guilty verdict by the jury in January 2003. If unsuccessful Fraser, 48, who was released on bail in May last year, will have to spend a further 22 years in prison.

Lord Gill, the Lord Justice Clerk, Lord Osbourne and Lord Johnston were told that vital evidence which might have cleared Fraser was not presented at his trial because of "extraordinary incompetence" rather than a cover-up.

Arlene Fraser has not been seen since she waved goodbye to her two children in April 1998. Fraser was sentenced to a minimum of 25 years after evidence was heard that he employed a hitman to murder her and then disposed of her body. The appearance of his wife's wedding, engagement and eternity rings in the bathroom of her home nine days after she vanished was the cornerstone of the Crown case.

The Crown's submission was the rings were not in the house when a police video was shot early in the investigation and that when they reappeared on a soap dish in the bathroom they had been put there by Fraser. His intention, it was alleged, had been to create the impression Arlene had run off to start a new life.

However, Peter Gray, QC, representing Fraser, told the appeal that Police Constable Neil Lynch, who has left the force, had indicated in a statement in 2002 that he believed he had seen the rings in the bathroom, where they were eventually found by Arlene's mother, on the first night after Arlene's disappearance.

The lawyer claimed that information had not been disclosed to the defence.

He argued that his client's trial was unfair because of the Crown's failure to disclose the information which could have had a significant impact on the conduct of the trial.

He revealed that a second police officer, Constable Julie Clark, had told an inquiry into the investigation in 2006 that she, too, believed she had seen rings in the bathroom of the house during the first night after Arlene disappeared.

Mr Gray told the court that a precognition officer took the statement from PC Lynch in 2002. He recognised the potential importance of the information provided by the policeman and requested that the trial prosecutor be made aware of it, Mr Gray said.

"It would appear that that simply did not happen," he said. He said Mr Turnbull told a subsequent high-level inquiry into the case: "If, in the course of the trial, I had been shown... Lynch's precognition, then I honestly would have fainted, so inconsistent would it be with my thinking and view of the evidence.

"If the Lynch precognition had come to light during the trial it is clear the trial would have had to be deserted. There would have had to be further Crown inquiry and defence precognition."

Mr Gray said the Crown informed the defence on March 7 last year about PC Lynch's information on the rings, as well as the evidence of Constable Clark.

The Crown's position was made public four days later.

A spokesman for the Crown Office and Procurator Fiscal Service said at the time: "In preparing the Crown's response to this appeal, Crown counsel learned that evidence which was relevant to the case was not made available to the defence or to the court at the time of the trial. Crown counsel considered that this evidence should be made available to the defence under the duty which the Crown has to disclose evidence which undermines the prosecution case or may assist the defence."

The appeal continues.