MODERN detective methods have been applied to one of Scotland's greatest historical mysteries in a new book which suggests that the Appin murder was not the work of one man, but a carefully conceived Jacobite plot.

The unsolved murder of Colin Campbell, the "Red Fox" of Glenure, in 1752 formed the subject of Robert Louis Stevenson's famous novel, Kidnapped, and has now been re-examined through original sources and contemporary policework.

Although James Stewart - James of the Glens - was arrested and hanged as an accessory to the murder of this notorious government agent, historians have argued for decades over who actually fired the shot. The prime suspect was the famous Jacobite, Allan Breck Stewart, who laid low during a manhunt then escaped to France.

Ian Nimmo, journalist and chairman of the Robert Louis Stevenson Club, has spent 40 years working on the book, Walking With Murder: On The Kidnapped Trail, published this month by Birlinn.

With the help of retired detective inspector Les Liney, Nimmo applied modern analysis techniques to two ancient postmortem reports from the National Library of Scotland and the murder scene in the Wood of Lettermore.

Nimmo has been determined to get to the heart of the matter since spending his schooldays in the area. "I was intrigued by the last great Scottish mystery, a murder for which an innocent man was hanged in the blackest mark of Scottish legal history, " he said.

"With the help of postmortem reports by two Campbell surgeons, I believe Les Liney has cast new light on the murder. Everyone thought that the bullets came from high on the hillside because of evidence from Mungo Campbell - Colin's nephew - saying that he saw a figure there with a gun going away from him.

"But the position of the bullets suggests they were fired from lower down, by an assassin on one knee in a nearby depression who could be out of sight in the trees in 10 seconds. We believe that the person on the hill was an observer, who left as soon as the job was done."

There was one shot but two wounds to Glenure's body because two bullets were loaded into the same gun barrel, the second called a wanderer - fear siubhail - as it was less accurate. Both exited his body, suggesting they were fired from close range, and from low on the hillside, according to Liney's analysis.

Nimmo also examined accounts of John Mackenzie, a servant travelling with the eviction party , and believes that he was part of the Jacobite plot.

Talking to descendants of the Mackenzie family, Nimmo discovered that at the time of the shot, the servant had left his master's side to pick up a coat dropped by the sherriff 's officer.

"The impression I was clearly given was that John Mackenzie's sympathies lay with the Jacobites and he knew exactly what was going to happen, " he said.

"Texts called the Dewar Manuscripts also mention a shooting match at which the Stewart gentry were looking to find the best shot and gun. There is no evidence to link this to the murder, but I believe there is a distinct impression of a Jacobite plot."

Nimmo said about 20 Scots have had first-hand accounts of the truth of the matter.

According to his research, the secret has been handed down through the Stewart family for 250 years, and he believes several living people have been told the murderer's name.

Nimmo believes the balance of evidence suggests that Breck didn't pull the trigger, but his book, which retraces the journey of Stevenson's heroes David Balfour and Alan Breck across Scotland, does not reveal who did. "They have held this secret for 250 years, and so I believe that it is not mine to give away."

Dr James Hunter, author of Culloden And The Last Clansman and director of the University of the Highlands and Islands's centre for history, said:

"This was indisputedly an act of political terrorism that brought tremendous reprisals, but neither I nor Ian Nimmo can be absolutely certain of who did it.

"I think there was a conspiracy among the Stewart gentry, with its roots in Jacobism and a longstanding family feud. There is no proof that there are people who know the name of the murderer, but I do not regard this as impossible."

The book will be launched at an Edinburgh International Book Festival debate with the sculptor Alexander Stoddart, on Monday, August 29.

senay. boztas@sundayherald. com www. edbookfest. co. uk