Michael Ross, found guilty of the 1994 shooting of Bangledeshi waiter Shamsuddin Mahmood in 2008, has outlined his version of events for the first time, after declining to give evidence at his trial.
In the letter to supporters, 35-year-old Ross said: "I did not kill Shamsuddin Mahmood and had nothing to do with his murder."
Ross, held at Shotts Prison in North Lanarkshire, added he had "never encountered" or heard of Mr Shamsuddin, a waiter at the Mumtaz Indian restaurant in Kirkwall, and only realised the seriousness of the situation "when I was taken away from school one day by the CID".
He added: "If I had the chance again, I would give evidence."
The Scottish Criminal Cases Review Board is due to rule whether to allow Ross to appeal against his conviction. A court ruled that Ross was the balaclava-clad gunman who shot Mr Mahmood in June 1994 when he was an army cadet.
Mr Mahmood's family called the claims in Ross's letter "ridiculous and offensive".