DRUG dealer Paul Cullen was shot twice in the head as he slumped to the ground after being hit by a barrage of bullets in the upper body.
The "execution-style" killing lasted a total of 22 seconds, it emerged last night.
Gardai believe that the gang used a spotter to pinpoint where the victim was sitting in the Cabra House pub before he was murdered in front of his wheelchair-bound father and brother.
Cullen, who lived across the road at Fassaugh Avenue, was sitting with his family to the left of the front door after watching the Premiership clash between Arsenal and Tottenham on TV.
The masked gunman burst into the pub, turned to his left and unleashed six shots, initially hitting Cullen in the upper body but as his victim fell to the floor, he fired the final shots into his head.
Cullen was a former associate of gang leader Eamon Dunne, who was shot dead at another Cabra pub, the Fassaugh House, in April 2010.
Gardai said last night that Cullen had built up a long list of enemies since Dunne's murder and they were pursuing several lines of inquiry to establish a motive for his clinical murder.
Cullen was said to have acted as an enforcer for a number of criminal groups active in the area.
But it was thought more likely that he had fallen foul of a drug trafficking gang over unpaid debts.
Cullen had previously been warned that his life was in danger. A judge in a court case in 2008 in which he was sentenced to six years' imprisonment, with 18 months suspended, for storing cannabis resin in his home, was told that he had received a bullet in the post and was attacked by criminals because of a €5,000 cocaine debt.
He was released from prison late last year after completing his drugs sentence and another 18 months for an assault on a female garda.
Gardai spent yesterday trying to track down and interview two dozen customers and staff, who were in the pub when the gunman ran in.
A number of the customers scattered for their own safety when the shots were fired and officers were attempting to locate those who they had not yet contacted.
Officers said they also wanted to interview anybody who was on Fassaugh Avenue between 6.30pm and 7.30pm on Sunday and saw two men acting suspiciously on a motorcycle.
The gunman left the scene on the back of the motorcycle, which was driven away erratically.
Gardai hope residents in the area may be able to help them identify the route used by the killers in their escape.
They have appealed to anyone with information to contact them at the investigation headquarters at Cabra garda station, 01 6667432, or on the confidential line, 1800 666111.