Gardai are now investigating any links between the attack last year and threats issued to Cannon over the past 12 months. The dead gangster was warned that his life was in danger on a number of occasions, it is understood.
Officers working on the murder case have compiled a dossier of over a dozen serious incidents that Cannon was involved in over the past 12 months, all related to the notorious Crumlin gang feud. The murdered gangster was a leading member of the gang opposed to Thompson's outfit in the feud.
He was a suspect for a shooting in Drimnagh three weeks ago, when a man was injured in the leg after being shot through a downstairs window at his home.
This man was suspected of involvement in the murder of Shay O'Byrne, a close pal of Cannon's, in Tallaght last March.
Gardai believe that the Drimnagh shooting three weeks ago may have been in retaliation to that murder.
However, senior sources said that finding a single motive for the shooting would be difficult, as Cannon was involved in widespread criminal activity. This included attacks that were related to the Crumlin feud, and other activity such as collecting drug debts and intimidation of drug users and other minor criminals.
Among the dossier of feud-related activity compiled by gardai is an incident on March 15 last year in which Thompson's home in the Coombe was attacked by Cannon and another man, who arrived at the scene armed with machetes and an iron bar.
The pair demanded entry to the house, but were refused and told Thompson was not home by the occupants, who barricaded the door. They then broke windows at the property with a machete before travelling to Bride Street, where they attacked the home of a Thompson associate, believing he was at that house. Windows were also broken at that property but no one was injured.
Gardai investigated the attack, but charges could not be brought due to lack of evidence.
Three months later, Cannon's name again emerged as a suspect for a shooting at the home of Freddie Thompson's grandfather, also in the Coombe. No one was injured in that attack.
Cannon was shot dead as he ran for his life at St Mary's Avenue, Ballyfermot last Friday afternoon. He was hit nine times by a gunman who fired 11 shots, having pulled up alongside him on a motorcycle. He incurred at least two fatal head wounds, and was wearing a bullet-proof vest when found.
His murder was the 17th gun killing of the year, and the 12th associated with the Crumlin gang feud.