Colin McKay owed a man named O'Hara £2000 for heroin. Instead of cash, O'Hara agreed to take payment in kind - he asked McKay to kill a rival named Peter McDowall.

Without debate, McKay agreed. On the day in question he ambushed McDowall, killed him in the most horrific manner then calmly phoned O'Hara to tell him the deed was done. CCTV footage of O'Hara near the scene caught him on his way to see the dead McDowall for himself.

Locals learned of the execution very quickly and within minutes McKay himself became the hunted prey as a group of furious men gave chase. They caught him, beat him and knifed him with the same blade he'd used on McDowall. McKay almost died as a result of the attack but survived to face the murder charges.

The jury took little time to find him and three others guilty. Of O'Hara, the sentencing judge said: "You literally terrorised a whole area of the city of Glasgow and reaped substantial rewards. "There is little I can say to reflect the revulsion every decent citizen must feel about you."

But the judge saved his strongest words for Colin McKay, "When O`Hara asked, you killed for him, as casually as if he asked you to get him a pint of milk. You are no better than a hired assassin."

In 1997 McKay and a man named Frank `the ice man` McPhie were accused of strangling newlywed Christopher McGrory, 25, in a row over drugs.

They walked free after a jury returned a not proven verdict but McPhie, 51, was shot dead by a sniper outside his home in Maryhill, Glasgow, in 2001. His killer has never been found.