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Officially Scotland’s longest-serving inmate Mone, was inside Carstairs when along with Thomas McCulloch, he took part in the infamous breakout that resulted in a bloodbath.
In 1968, then aged 19, Mone was sent to the State Hospital after being charged with killing schoolteacher Nan Hanson.
He was found to be insane and unfit to plead at that time and was ordered to be detained in hospital where he met McCulloch.
The pair staged a daring escape in November 1976 during which a nursing officer, a patient and a young policeman were butchered to death.
Mone was then found to be sane.
He admitted axing constable George Taylor to death, but his not guilty pleas to the other murders were accepted.
The judge, Lord Dunpark, described the men as “the most deliberately brutal murderers” he had ever had the misfortune to deal with and said in their case life should mean life.