A LEADING criminologist has called on Police Scotland to release details of key evidence surrounding one of Scotland’s most baffling murders in an attempt to flush out fresh witnesses.

Speculation has mounted over an envelope handed to Nairn banker Alistair Wilson, 30, by a gunman before he was shot on his doorstep 12 years ago.

At about 7.15pm, the killer rang the doorbell of the Wilsons’ home in Highland as Mr Wilson and his wife were preparing their sons, Graham, four, and Andrew, two, for bed.

The caller was described as being about 5ft 4in-8in, of stocky build and wearing a baseball cap and dark blouson jacket.

He had asked for Alistair Wilson by name when wife Veronica had opened the door that evening. She went back inside and told her husband, who went to the door and spoke to the man, then came back into the house with a blue or green A4 envelope. When he returned to the door he was shot, and the envelope was never seen again.

Police Scotland has consistently refused to give any more information about the envelope or the conversation between the Wilsons on the night of the killing.

They said they remain “absolutely committed” to finding the man responsible for the unsolved murder, which took place on Sunday, November 28, 2004.

But David Wilson, professor of criminology at Birmingham City University, said that given the length of time that had elapsed without any major progress being made in finding Mr Wilson’s murderer, police should now release any unpublished information on the envelope.

He told the BBC it could be key to unlocking 12-year-old case.

“Police have steadfastly refused to release details of what might have been in the letter,” said Mr Wilson.

“It is my understanding there was a conversation between Mr and Mrs Wilson about what the letter contained.”

He understood that holding back some piece of key information was a recognised way of establishing whether people coming forward genuinely had information that would help, or were just wasting the police’s time.

But Mr Wilson, himself a Scot, said: “I think given how old this case is, one of the keys to unlocking it might be for Police Scotland to talk about what was in this letter.”

Police said there was no change to the position on the contents of the letter.

A spokeswoman said: “Following a review of the Alistair Wilson murder under homicide governance processes introduced by Police Scotland, the investigation remains active and ongoing.

“We will consider all forensic and investigative opportunities.

“We remain absolutely committed to tracing the person responsible for Alistair’s death and continue to ask the public for any information which might assist us.”

The gun in the shooting was found 10 days later in a drain in Seabank Road, Nairn, by council workers cleaning a gully.

It was established to be a Haenel Suhl Model 1 Schmeisser patent handgun, made between 1920 and 1945 in Germany. The ammunition was .25 calibre and made by Sellier & Bellot, between 1983 and 1993, in what is now the Czech Republic. However, this apparent breakthrough did not lead police to the murderer.

It was the same with a cigarette end found on the doorstep with a DNA structure that could not be identified, despite more than 1,000 samples being taken.