The appearance of the three gold rings belonging to Arlene Fraser more than a week after she vanished more than 13 years ago was the "cornerstone" of the case against Nat Fraser.

Yesterday, the same matrimonial jewellery appeared to be its undoing at the UK Supreme Court.

The Crown had convinced the jury at Fraser’s murder trial in 2003 that the three rings -- one for engagement, another for marriage and a third for eternity -- had been placed by the accused in the family bathroom to create the sense that his wife had removed the pieces of gold to symbolise she was walking away from her husband.

But a police officer’s precognition statement, given under oath ahead of the trial, dramatically undermined the Crown’s position.

Nobody in the court, including the advocate depute and, crucially, Nat Fraser’s defence team, knew about this evidence.

PC Neil Lynch claimed in the statement he had seen a bracelets and rings in the bathroom in the Fraser household on the night Fraser’s wife disappeared, before a police search began.

His colleague, WPC Julie Clark, later concurred with her colleague’s remarks, claiming she too had mentioned this during her precognition.

The recollections were at odds with the contents of the officers’s notebooks and their earlier claims. Despite an intention that PC Lynch should come back to the police station at Elgin and identify the rings, the claims were never fully followed up.

In 2006, Nat Fraser started proceedings to challenge his conviction in the Court of Appeal. The first ground was that the officers’ evidence was new and, as it was not heard by the jury, he was a victim of a miscarriage of justice. The Crown’s failure to disclose PC Lynch’s evidence to the defence before the trial had the same result, Fraser claimed.

In 2008, Lord Justice Clerk, Lord Gill, ruled that the officers’ evidence was not new but, even if it was, the verdict could not be regarded as flawed. Fraser, freed from jail pending the appeal, was back in prison.

Lord Gill played down the precognition statement, saying that “even at its highest” PC Lynch and WPC Clark’s evidence had no material significance in comparison with evidence of family members and the circumstantial background to the case.

But it was this crucial position that the Supreme Court, which considered Fraser’s right to fair trial under Article 6 of the European Convention on Human Rights, undermined.

Lord Hope, Deputy President of the court, stated in his judgement yesterday: “The proposition that the appellant had returned the rings to the bathroom on May 7 was, as the Advocate Depute said in his address to the jury, the cornerstone of the Crown’s case.”

He went on to say: “The fact is that the Crown chose to present the case at the trial in a way that it would not have chosen to do if it had been aware at the time of the trial that there was evidence that the rings were in the house within hours of Arlene’s disappearance.

“Nor is it an answer to say that the obligation of disclosure does not extend to precognitions in the possession of the Crown.

“This is because the evidence as to the presence of the rings in the house on that night had such an obvious bearing on a crucial part of a circumstantial case against the appellant.

“It does not matter where the material was to be found.

“It was information that ought to have been given to the defence, and the failure to do this was a breach of the appellant’s Article 6 right.”

Lord Gill said in 2008 that he was not persuaded that the recollections of either officer could be regarded as reliable.

However, Lord Hope found that disclosure of the material would have opened up lines of cross-examination that were never pursued by the defence.

“It would also materially weakened the Crown’s attack on the appellant that he had no explanation to give for bringing the rings back to the house on May 7 and the theory that he had retrieved them from Arlene’s dead body. He would not have had to provide an explanation if, as the evidence of PC Lynch and WPC Clark suggested, the rings were in the house all along.

“Of course, the reliability of their evidence would have been called into question. But so too would the reliability of the evidence for the Crown, including the video that was taken during the police search of the bathroom,” he said.

The rings were not captured on the police video.

The theory that Nat Fraser removed the three rings from the dead body would be “untenable” if the officer’s evidence had been accepted, Lord Hope said. If that had been the case, the defence arguments would be able to “strike at the heart” of the Crown case.

Lord Hope concluded. “The trial would have been significantly different had the material that was not disclosed been available.

“There is a real possibility that this would have been sufficient to raise a reasonable doubt about the Crown’s case that the appellant returned the rings to the bathroom on May 7. If that were so, the jury’s verdict would be bound in view of the trial judge’s direction to have been different.”