Walker was released from maximum security to a care home after suffering an incapacitating stroke in 2011.
While serving his sentence at HMP Shotts in Lanarkshire, Walker was considered one of the country’s most dangerous inmates. He would brag about having buried £19,000 in cash in the Pentland Hills and persuade fellow prisoners to do him favours with the promise of a payday from the stolen payroll.
On January 17, 1985, retired Major David Cunningham, 56, Staff Sergeant Terence Hosker, 39, of the Royal Army Pay Corps, and Private JohnThomson, 25, of the Kings Own Scottish Borderers picked up the payroll from the RBS in Penicuik to take to Glencorse Barracks.
Walker, then a 30-year-old corporal in the Royal Scots, flagged down their Land Rover and asked for a lift back to barracks.
Earlier, he had signed a sub-machine gun from the armoury which he pulled on the trio and ordered them to drive into the nearby Pentland Hills.
Sgt Hosker bravely tried to tackle Walker but was fatally shot in the head and chest.
After ordering Pte Thomson to drive along a quiet track to Flotterstone Reservoir, he shot Major Cunningham through the head.
Thomson was then forced to unload the bodies of his colleagues before being shot himself in the head and arm.
The payroll cash was never recovered and Walker – who was quickly identified as the prime suspect – went on the run before being captured three days later.
When questioned Walker, who had served three tours to Northern Ireland and once earned a mention in dispatches, blamed the murders on trauma from past military experiences.
However, it soon emerged that he owed £2,000 on a car repair bill and about to take delivery of a new one worth £8,500, and was motivated purely by money. He was also overdrawn at the bank and had tried to borrow money from fellow soldiers.
Walker denied his guilt but was convicted by a jury and ordered to serve a minimum 30 years before applying for parole, at the time Scotland’s longest sentence. He was subsequently handed another 9 years for his role in the 1986 Peterhead Prison siege and riot, which was ended when the Aberdeenshire jail was raided by the SAS.
Despite regularly contacting newspapers and boasting to fellow convicts about his ‘buried loot’ Walker never revealed where he hit the stolen £19,000. A number of searches were carried out but all failed.
The mystery may never now be solved after walker passed away aged 67 at Murdostoun Castle care home in Wishaw, Lanarkshire, from suspected cancer and another stroke.
In her most recent interview, in 2019, Pte Thomson’s widow Susan, who was 19 when her husband was slain by Walker, said: “Each year he lives on, I get angrier.”
Ms Thomson had previously described the decision to admit Walker to a care facility ‘a mockery of justice’.