ONE of Scotland's most famous murder cases is still shrouded in mystery despite attempts to crack it using modern forensic techniques.

Experts who studied the ­available evidence relating to the 1752 Appin murder concluded James (Stewart) of the Glen, hanged for the crime, was not guilty, and the person identified as the main suspect was not responsible.

However, no new suspects emerged for the shooting of Colin Campbell of Glenure in the woods of Lettermore, near where the Ballchulish Bridge now stands.

Experts invited to re-examine the case by the Royal Society of Edinburgh said the evidence pointed to two unknown gunmen, not one, having killed Campbell.

The murder was central to the plot of Robert Louis Stevenson's Kidnapped. In it a man with a gun is seen running away up a hill. When David Balfour follows him, he finds his one-time travelling companion, Ailean Breac Stewart, armed only with a fishing rod.

The expert group comprised of respected scientific, legal and academic figures, led by forensic anthropologist Professor Sue Black of Dundee University. She said: "We were looking at the evidence and the fact as portrayed in the trial in Inveraray. Everything else was hearsay or circumstantial."

She said there was a re-examination of the medical, ballistics and identification evidence using modern techniques.

This was presented by retired judge Lord Cameron of Lochbroom to more than 100 members of the public, who formed the jury. She added that the original ­indictment named Ailean Breac Stewart (Allan Breck in the book) as the guilty party for murder, and James Stewart as guilty of abetting him. She said that for Ailean Breac to have been guilty, evidence as to his whereabouts that day had to be examined.

She said: "The panel (of experts) agreed he could not have been the man on the hill."

The look at the ballistic and medical evidence revealed the two shots, thought to have come from one musket, had come from two. Ms Black said: "We asked if there was any evidence Ailean Breac was responsible for pulling one of the triggers, and the answer was no. We asked if there was any evidence he was at the murder scene, and the answer was no.

"Lord Cameron put a ­proposition to the jury that they must return a verdict on whether there is sufficient evidence to uphold the indictment that Ailean Breac Stewart was guilty of the murder. They were asked if they had heard evidence that supported the indictment, and not a single person put their hand up.

"If they didn't uphold the ­indictment, then there shouldn't have been a case against James Stewart. If Ailean Breac didn't commit the murder, how could James have abetted him?"

She said an eyewitness knew what Ailean Breac looked like, yet did not recognise him as the man on the hill. Evidence Colin Campbell was shot from behind was also questioned.

Professor Dave Barclay, formerly of the forensic science department at Robert Gordon University in Aberdeen, said the type of musket used could fire two shots, but it was unlikely as they would not have had the required power and accuracy.