Joe Steele was cleared of the slaughter of six members of the Doyle family in Ruchazie 20 years ago today.
Now he says that McGraw, nicknamed the Licensee, was in some way responsible for the arson attack that brought the drugs turf war - usually using ice cream vans - to its culmination.
Mr Steele said he would have killed himself had he been responsible for the murder. Victims included 18-month-old Mark Halleran, nephew of Andrew "Fat Boy" Doyle, an ice cream van driver and the main target.
Speaking in an internet documentary, Mr Steele said: "I believe Tam McGraw was involved . I don't believe he lit the match - but he was behind it.
"To be accused of killing a family, a kid - if I had done that I would have topped myself." McGraw died in 2007 or heart failure.
Mr Steel was convicted in 1984 of the killings along with co-accused Tommy "TC" Campbell. They had protested their innocence and won a 20-year battle to clear their names in March.