Detectives investigating the murder of innocent Limerick businessman Roy Collins now believe he was killed after refusing to allow members of the McCarthy-Dundon crime gang deal drugs at his family's amusement arcade and adjoining pub.

Men aged 19 and 22, arrested in the connection with Collins' murder, had their period of detention extended by 72 hours yesterday. Follow-up searches in Limerick are set to continue all weekend.

Gardaí also suspect that a long-held grudge by the criminal gang over Collins' cousin testifying against gangland figure Wayne Dundon in 2005 was a factor in the murder.

The McCarthy-Dundon crime gang have long memories. It's inconceivable that a barman's refusal to serve a 14-year-old alcohol in 2004 could have led to the murder of his cousin five years on.

But this is what initially sparked last week's violent killing – it cemented a deep hatred of the Collins family by Limerick's most dangerous criminal gang.

In recent weeks, there had been run-ins between the murdered man, his family and members of the McCarthy-Dundon gang, as the father-of-two had steadfastly refused to let them sell drugs or hang around the family's business premises.

"There have been run-ins. The Collins family have always stood up these criminals and refused to be intimidated by them," according to a garda source. The refused to succumb to these criminals since day one and have strong views about their criminals activities."

It is understood that gardaí are investigation words exchanged between the dead man's family and the criminals on at least two occasions in recent weeks when they were ordered them off the premises of the Steering Wheel pub.

Limerick, once again, is left to try and shake off its image as a city where a group of criminals kill as they please without regard or fear for the authorities.

Collins was a cousin of Limerick man Ryan Lee, but they were raised as brothers. Collins's father, Steve Collins, became Lee's legal guardian. Lee was working as a barman in Brannigan's pub, Mulgrave Street, Limerick in 2004 when he refused to serve to a 14-year-old girl.

The teenager was the sister of well-known criminal Wayne Dundon, who was with her at the time. He was so enraged that someone dared tell him 'no' that he made a shape of a gun with his hand and pushed it against Lee's face, saying "f*** you, you're dead".

Minutes later, a man wearing a helmet entered Brannigan's pub armed with a sawn-off shotgun. The gunman immediately honed in on Lee and shot him twice in the knee and hip.

The Collins family owned Brannigan's pub where Lee was shot. It was burned down shortly after Wayne Dundon was jailed for threatening to kill Lee and never re-opened. Dundon (31) was sentenced to 10 years in 2005 for threatening Lee, which was later reduced to seven years.

Lee gave evidence in court against Dundon, which ultimately led to his conviction, but no one was ever convicted of shooting the 19-year-old barman.

With remission, Dundon will most likely be back on the streets next year. The violent thug is considered one of the most dangerous criminals to emerge from Limerick.

After Dundon's conviction, it emerged that Lee's girlfriend received a threatening letter the night after the jury was sworn in for the trial. The letter was addressed to Steve Collins, Roy's father.

The letter threatened to attack Collins's staff and his business and also warned him "to look at all the other people that's dead". While these threats were made in 2005, senior gardaí maintain that once the McCarthy-Dundons make a threat, it's never forgotten.

"It's early days in the investigation. We believe Lee Ryan testifying against Dundon was never forgotten but this killing didn't come out of nowhere. Collins had continued to defy them by not allowing them to have free rein of doing as they pleased on his premises," according to a senior officer.

"They hated him and they wanted him dead. He might not have been killed if he hadn't continued to stand up to them. The people responsible for this killing were senior members of the McCarthy-Dundons. They are young men with no education, no class, no minds of their own. They would not have been paid for killing him, unlike Dublin criminals that won't do anything without getting paid. They killed him to keep the others happy and bolster their reputations in the gang."

Gardaí have provided protection to Lee and the rest of the Collins family since Dundon's trial. Stephen Collins spoke to defence minister Willie O'Dea about threats made against him just days before his son's killing.

"I was approached on a number of occasions by Roy Collins' father recently in relation to threats in connection to which he was getting garda protection. But I never realised for a moment that another member of the family could actually be gunned down, somebody who had nothing to do with the original court case," said O'Dea.

One of the men in custody in relation to Collins murder was the person who drove the car used in the murder of innocent rugby player Shane Geoghegan five months ago. Bizarrely, the 19-year-old accepted the Sunday Tribune's 'friend' request which gave us access to his personal Bebo profile in November.

Although the teen was then on the run and hiding in the UK, he was still in constant contact with his family, friends and criminal associates. The web page offers a compelling but disturbing view of the interests of the man, who is from the Prospect area of Limerick and is a senior player in the Dundon-McCarthy gang, despite his youth.

The teenager is fascinated by guns and has photos of more than a dozen lethal weapons, including the Glock 9mm pistol, which was used in the murder of Geoghegan. "The fact that the McCarthy-Dundons are responsible for the killings of two innocent men in Limerick in such a short space of time has solidified them as far more ruthless that the Keane-Collopy gang," according to a garda source.