Nothing will stop these gangs from bloody revenge...

His best pal, Graham Whelan, had been in custody for two days being questioned about the gangland assassination of suspected hitman Gary Bryan. Subsequently, Whelan was never charged in connection with the Bryan murder.

Byrne gave the sergeant in charge a copy of the Evening Herald and when the officer flicked through it he noticed a message on the top of a page. It read “loose lips sink ships”, a warning the then 24-year-old was giving to his pal – never, ever talk to gardai or betray your friends.

It was this mentality of fierce loyalty that ultimately led to the feud that would cost Byrne his life.

The seeds of the current feud between the Kinahan and Hutch gangs were sewn in August 2001 when young gang leader Declan Gavin was stabbed to death in the Abrekebabra restaurant in Crumlin village. One of the last people to speak to him before he died was David Byrne who was queuing for chips. Gavin was murdered after he was wrongly accused of being a “rat” to gardai, by giving information about a drugs seizure.

This led to a group of childhood friends splitting in two and resulted in a series of tit-for-tat murders over the next 12 years.

David Byrne took the side of his first cousin ‘Fat’ Freddie Thompson in the feud. They were fiercely loyal to each other and didn’t trust outsiders. The gang ultimately answered to the ‘Dapper Don’ Christy Kinahan, a drugs godfather based in Spain who supplied them with cocaine which they flooded the streets of Dublin with.

David Byrne was an active feud member along with his brother Liam. In June 2002 he was the target of a gun attack in Dublin 8 but escaped injury. He also had a narrow escape in 2009 when a bomb was found under a car near his home. Since that incident he kept a lower profile and began to learn his trade as a “logistics man” for the Kinahan gang, organising safe passage into Ireland for massive drugs shipments by making contacts with legitimate companies and using trucks to safely bring in product.

Whereas ‘Fat’ Freddie courted publicity and seemed to revel when his face frequently appeared on the front of the Herald, the Byrne brothers kept a low profile and made themselves indispensable to the Kinahans because they were good at what they did and made the mob a hell of a lot of money.

So where Freddie played the public role of the gangster, the Byrnes were the brains behind the scenes. They were back and forth between Dublin and Spain and became close to Daniel Kinahan who effectively took over his father’s drugs empire in May 2010 after Spanish police moved to smash the gang and uncovered assets of over €500m.

The three, along with Gary Hutch, a criminal from the north-inner city who was a nephew of the infamous Gerry ‘The Monk’ Hutch, made lots of cash and effectively operated under the radar except for the odd mention in the media.

Then things unravelled. Suddenly the gang began to find their drugs shipments seized by gardai, something that never really happened before, mainly thanks to David Byrne’s planning expertise. In all around five shipments were seized from the beginning of 2014 and the gang began to suspect there was an informant in their ranks.

The finger was pointed at Gary Hutch. He didn’t have the relationship going back to childhood like many of the other criminals and he was seen as being too loyal to other hoods from the north-inner city. In late 2014 a decision was made to expel Hutch from the Kinahan gang because even the whiff of suspicion about being an informant can be fatal.

A deal was brokered through associates of The Monk and Gary Hutch was given an €800,000 severance package and assured he was safe.

He bought an apartment in Mijas, but was shot dead last September by the Kinahan cartel. The murder was the first time that a member of the extended Hutch family had been targeted in the four decades the family name had been known to gardai.

The fact that the Kinahans so blatantly breached a binding handshake agreement was bad enough, but when the gang demanded €200,000 in “compensation” from one of Gary Hutch’s relations all bets were off.

There was no way back and senior members of the Hutch gang knew it was either kill or be killed. The Regency Hotel murder had echoes of the audacious robberies that associates of Gerry Hutch carried out in the 1990s. But Daniel Kinahan was the main target and the fact is that he remains on the street – so the attack ultimately failed.

The swiftness and viciousness of the retaliation, when innocent taxi driver Eddie Hutch was gunned down at his home, is likely to lead to an escalation of the feud and peace just does not seem feasible.

With one innocent man dead gardai have real fears that other non-combatants will now be targeted and that is a nightmare scenario for gardai and the government.

Armed gardai will flood Dublin this weekend and early next week until the funerals take place, but then things will go back to normal. And as both gangs have shown over the last eight days nothing will prevent them from seeking bloody revenge and this feud has the real potential to become Ireland deadliest ever.

Mick McCaffrey is news editor of UTV Ireland and has written three best-selling true crime books