It all started with a drink thrown in a nightclub. It led to four years of bloodshed, including two murders, at least seven shootings and an escalation of tit-for-tat violence reminiscent of the “Gunchester” era of the 1990s.

Mark Fellows, 38, became one of only 70 prisoners in England and Wales serving a whole life sentence on Friday after he was found guilty of the murder of his gangland rivals Paul Massey and John Kinsella.

The Salford hitman, nicknamed “the Iceman” for his calm exterior, fired 18 bullets with an Uzi submachine gun at Massey in July 2015 before shooting dead his associate, Kinsella, three years later.

The execution-style murders shocked the criminal underworld of north-west England. Massey, 55, had made his name selling drugs in Manchester’s 1990s rave scene but remained a known “face” in Salford.

Kinsella, 53, was respected and feared in equal measure, having intervened when a gangster threatened “to maim” the former England footballer Steven Gerrard. The Merseyside enforcer was a pallbearer at Massey’s funeral.

The unsolved murder of Massey loomed over Greater Manchester police for three years. Detectives had 112 names as possible suspects – a who’s who of the Salford underworld – while facing a wall of silence from the public who feared repercussions if they spoke.

Mark Fellows’s victims: Paul Massey, left, and John Kinsella. Composite: PA/Rex/Shutterstock

Even when a seven-year-old boy and his mother were shot in their legs on their doorstep as the feud escalated, no witnesses were forthcoming. It made solving the murder more difficult than policing the notorious violence in Manchester’s Moss Side in the 1980s and 90s, Salford’s police chief told the Guardian at the time.

DCI Carl Jones, who worked on the Massey investigation, described it as “probably the most taxing and at times frustrating” case he and his team had ever faced. “When you have organised crime incidents, the obvious thing is people will not speak. You have the frustration of the victims’ families who want us quite rightly to solve it quickly. It’s sensitive and complex – it’s so frustrating.”

The murders were part of what police described as a war between the rival Salford gangs the A-team, which was associated with Massey, and the anti-A team. Detectives believe it started when a woman threw a drink over a member of the A-team in a nightclub in summer 2014.

Months later, the roof of a woman’s VW Golf car was hacked off using a Stihl saw. The violence escalated into a year of chaos, said DCI Jones, as a shotgun was fired into a car, injuring one man, before another victim suffered horrific injuries in a machete attack.

Mourners attend the funeral procession of Paul Massey in Salford in August 2015. Photograph: Peter Byrne/PA

In March 2015, a hand grenade was thrown at an A-team family member’s house, luckily exploding outside the property. A series of reprisal shootings followed as detectives struggled to contain the violence.

Fellows was already in the frame for Massey’s murder when he gunned down Kinsella in May last year. The modus operandi of the killings was strikingly similar – execution-style shootings by a man believed to have fled by bicycle – but the breakthrough came when detectives investigating the Kinsella murder found a Garmin watch used by Fellows for long-distance running.

The watch, it transpired, had recorded the hitman carrying out a reconnaissance run shortly before Massey’s killing. Its data correlated with the hundreds of hours of CCTV and mobile-phone data that had been analysed by officers from both forces.

Steven Boyle was jailed for a minimum of 33 years after being found guilty of the murder of John Kinsella. Photograph: Merseyside Police/PA

There were gasps in the tight-security courtroom during the trial as Fellows’s associate, Steven Boyle, broke the gangland code of silence and “grassed” on him by telling jurors it was “more than likely” his former friend had done it. Fellows was later seen making a cut-throat gesture to his co-defendant.

Fellows now ranks alongside the serial killer Levi Bellfield and the Yorkshire ripper Peter Sutcliffe as one of only 70 prisoners in England and Wales serving a whole life term. His accomplice, Steven Boyle, was jailed for a minimum of 33 years after being found guilty of the murder of Kinsella but cleared of the murder of Massey.

Sentencing the men at Liverpool crown court, Mr Justice Davis said: “Whatever the background of Mr Kinsella and Mr Massey, the impact on their families of their murders has been devastating. This was execution, pure and simple.”