An image taken from Brian Rattigan's mobile phone in prison

They had been boyhood friends and lived just a stone's throw from each other in Drimnagh, a working-class suburb in south Dublin. That was before drugs and greed took over, the friendship ending with one fatal stab wound to the heart.

Brian Rattigan's conviction for the murder of Declan Gavin brings to an end a case that has dragged on for the best part of nine years.

Although justice has finally caught up with 28-year-old Rattigan – and he will pay for the murder with a life sentence – the repercussions of the night of 25 August 2001 live on.

Gavin's murder was the first killing in a feud that has now claimed 16 victims with little sign of an ending.

It is doubtful that Rattigan knew the consequences when he left Gavin lying dead on the floor of the Abrakebabra fast food restaurant on the Crumlin Road.

Because of his actions, his younger brother would be murdered eight months later and nine of his own friends and gang members would also lose their lives.

It began as a night of celebration for both victim and perpetrator. At the Rattigan household on Cooley Road a large group of family and friends gathered for the 18th birthday party of Joey Rattigan.

Less than two kilometres away, 20-year-old Declan Gavin attended a friend's 21st in the Transport Club in Crumlin before heading into town to Club M.

After making his way back to Crumlin at around 2.30am, Gavin and a group of his friends went to Abrakebabra for a burger. Back at Cooley Road some of the partygoers were hungry and three of Brian Rattigan's pals, including John Roche, drove to the fast food joint and ran into Gavin.

A heated verbal row ensued, with John Roche calling Decco Gavin a "rat" for allegedly tipping off gardaí about a drugs seizure in a hotel on Pearse Street 18 months before.

That seizure and another couple of incidents going back to 1998 had led to a group of 20 or so friends splitting and forming separate gangs, specialising in the sale of cocaine and cannabis. There had been non-fatal shootings and other incidents before the night of the murder but the feud had largely been minor and under control.

Declan Gavin stood up to Roche and shouted he was no rat. He maintained he would be going to jail for being caught with the drugs in the hotel. The group separated without any punches being thrown.

John Roche and his two friends drove back to Brian Rattigan's house and told him about the row with Gavin. Rattigan took a knife and a balaclava from his bedroom and went back with his friends to Abrakebabra.

Rattigan arrived outside the restaurant about 3.30am and spoke to two people he knew at the scene before seeing Declan Gavin.

Witnesses have variously described Rattigan as saying: "Decco, ye rat, you're dead", or "Decco, do you remember me?"

He then put on the balaclava and ran towards a surprised Gavin and stabbed him once in the heart with the knife.

Gavin staggered into Abrakebabra and managed to close the door on his attacker. Crucially, Brian Rattigan touched the glass and left his fingerprint on it. It was this piece of evidence that would eventually convict him.

Rattigan ran back to the car and the vehicle was attacked by onlookers and had missiles and a golf club thrown at it. Back in the restaurant Declan Gavin told the 20 or so shocked diners that he had been stabbed and he collapsed in the kitchen and later died in hospital.

The Nissan Micra which was used as the getaway vehicle was found burnt out the following morning at the nearby Cookstown Industrial Estate.

Gardaí immediately identified Brian Rattigan as the chief suspect. It was known there was bad blood between the rival drug gangs and several witnesses told officers off the record he was responsible.

They were too afraid to make official statements because of Rattigan's reputation. Rattigan was due in Dublin District Court on 4 September 2001 and when detectives tried to arrest him they were jostled by two of his relatives and he escaped.

When he was detained later that day and interviewed, he claimed he was with a married woman on the night of the murder but could not name her.

He also refused to take part in an ID parade, quoting the Bob Dylan song 'Hurricane' and saying that the boxer Ruben Carter was wrongly convicted. He also denied being near the Abrakebabra and said he hadn't eaten there for months.

When it was put to him that his fingerprint was found on the restaurant's front door glass he panicked and said if his prints were discovered in Gavin's blood then "it's all over".

He then regained his composure and predicted that if witnesses saw anything they would never say it in open court.

Before Rattigan was released without charge he told detectives he could guarantee he would not be charged with the murder. He threatened that gardaí would be going around in bulletproof jackets because "there will be another one [murder]. If I get done tomorrow one of them will get it, that's the way it is."

In October 2001, eight months after the Declan Gavin murder, gardaí at Crumlin seized a Volvo S40 that had been parked in the area for a number of days. It contained a shotgun and ammunition.

Garda intelligence indicated the car had been used by Rattigan and his gang to deliver drugs and store weapons in anticipation of a war breaking out over Gavin's murder. When Rattigan's fingerprints were discovered he was arrested.

He claimed not to know anything about the gun or his fingerprint saying: "You planted my print again like ye did at Abrakebabra." He then joked, "I'll have to get a pair of gloves."

When asked about the "gang warfare" because of Gavin's murder, he laughed and made a reference to the dead man: "I can't go out, that's why I am in the bunker [hiding]. I can't even go down to get a Decco kebab or a Decco burger."

When asked why he was laughing about a dead man he snarled: "F**k him, I hate him... I am not going to admit the murder or having that gun or anything. He had it coming... I did what I had to do... I'll not do time for him, no one will give evidence."

Gardaí pointed out he did not know for sure that witnesses would not speak in court and what would happen then. "I'll have to do the time, what can I get, 10 years? Ten years is nothing, time would fly."

He then spoke for the first time about what he did on the night of the killing. "I was pissed, I admit that. I had a load of Bud. I did about 20 lines [of cocaine] and I normally would be f**ked after that and fall asleep... Shit happened, I am not naming names, I am not going down that road, I can't tell you about the shopping centre [Abrakebabra]."

Although gardaí had little doubt that Rattigan had murdered Gavin, they were unable to gather sufficient evidence and the case effectively stalled with the DPP declining to press charges.

In the meantime, Rattigan was sentenced to nearly 12 years in jail for drugs and gun charges so he was off the streets although he continued to run his gang from prison.

In early 2005, a new garda inspector was assigned to Crumlin and reopened the case. Several new lines of inquiry were found.

The DPP then decided Rattigan should face a trial and despite the murderer using every possible legal avenue, the trial eventually went ahead and lasted over a month before the jury failed to reach a decision. A retrial was ordered.

Rattigan will now serve a life sentence and is unlikely to be freed until at least 2025.