Kinahan lieutenant Liam Byrne has been a target for the UK's top crime agency for up to six years.
Senior sources have told the Irish Mirror that the National Crime Agency's interest in the gangster was sparked by a garda raid which also brought down two other senior members of the mob.
Documentation seized by the gardai in a raid of the Greenogue industrial unit in west Dublin in 2017 was the beginning of the end for 42-year-old Byrne.
The Crumlin native is in Spanish custody as he fights his extradition back to England.
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He was arrested in Mallorca on June 4, on foot of an NCA warrant which claims the thug is believed to be involved in the supply and acquisition of firearms.
However, sources say that the Gardai from the Drugs and Organised Crime Bureau played a huge role in getting the NCA to target Byrne.
In January 2017, detectives from the DOCB raided the Greenogue industrial unit where 15 high-powered weapons were found and a later search then recovered €3million worth of heroin.
It saw the capture of the Kinahan's senior associate Declan "Mr Nobody" Brady, who is now serving lengthy sentences for firearms possessions as well as money laundering.
But it also saw the DOCB provide members of the NCA with crucial information after a logistics firm in the UK's midlands was identified from the papers.
This kicked off a major probe kick off in the UK and later saw Kinahan No2 Thomas "Bomber" Kavanagh, Gary Vickery, and Daniel Canning all identified as running a €36million drug smuggling scheme.
"Figurehead" Kavanagh, Vickery and Canning were sentenced to over 60 years between them in jail for their roles in the operation last year.
But unbeknownst to Byrne, who lived in Birmingham from 2017 and is Kavanagh's brother-in-law, he had become a priority target for the NCA during this investigation.
A source said: "Everything comes back to the gardai's raid on Greenogue in terms of Byrne.
"The information from documentation seized there was crucial in terms of the NCA becoming involved in the fight against the Kinahans.
"They were able to get enough on Bomber and his associates to bring charges against them.
"And although Byrne was very much involved and tied in with Kavanagh and the Kinahan's UK business, the NCA had to bide their time to get evidence against him before going for him.
"And that's exactly what they have done."
The documents seized by gardai in the Greenogue raid also identified a legitimate business in the UK which Kavanagh's gang had been using the name of.
The business, based in Manchester, had received a number of phone calls relating to the mob's dodgy business and later passed on numbers to investigators, which assisted the probe.
At the end of last month, Spanish authorities also arrested 22-year-old Jack Kavanagh, the son of Bomber Kavanagh, on behalf of the NCA but he is fighting extradition, like Byrne.
Investigators obtained the arrest warrants after they claim EncroChat messages showed both Byrne and Kavanagh were believed to be involved in the supply and acquisition of firearms.
The NCA are specifically focussing on a link to the find of 11 deadly firearms seized in Jerrettspass in Armagh in May 2021.
The "ready for use" weapons included hand guns, machine guns, machine pistols and an assault rifle.
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