Sources have revealed that just minutes before he was shot dead in the packed Fassaugh House pub, the gangster took a number of "serious" calls on his mobile phone.
One of these was from a jailed gangland criminal who is serving a life sentence for a brutal murder. He was in Mountjoy Prison at the time and called 'The Don' on an illegal mobile phone from jail.
A source explained: "This fella was convinced that Dunne was sleeping with his girlfriend. He confronted Dunne about this on the phone -- Dunne was his usual aggressive self with this man."
Just minutes later, 'The Don' was shot dead -- lying in a bloody heap on the floor -- abandoned by his own gang members who had fled the scene of mayhem.
It is understood that Dunne was not killed on the orders of the jailed gangster who has been arrested in relation to the slaying but instead a grouping of dangerous north inner city criminals were involved in what was the most significant gangland murder for years.
Dunne was sitting next to his then 17-year-old daughter in the Cabra pub on April 23, 2010, when two gunmen entered and fired up to a dozen shots.
One of the men walked up to Dunne and shot him a number of times in the back of the head and fired more shots after Dunne had hit the ground.
The second gunman, who was armed with a revolver, stood just inside the pub door with his gun at the ready to shoot anybody who tried to intervene.
Two other men waited outside the pub in a Volkswagen Passat getaway car, which was later found close to the pub.
The north inner city gangsters have extremely close links to the Christy Kinahan international crime network and may also have been given logistical support by a group of young Cabra-based criminals who are considered "extremely vicious".
Dunne had been in the Fassaugh House pub to celebrate the 38th birthday of his close pal John Fairbrother.
Mr Fairbrother had known psychotic gangster Eamon Dunne since they were children and the taximan was left devastated by the murder of 'The Don'.
In the aftermath of the shocking gangland murder, Mr Fairbrother described how Dunne's then 17-year-old daughter Amy stood over her father screaming "me da, me da" as his bullet-ridden body slumped to the floor.
He described the noise from the firearm as "like Chinese fire-crackers going off".
Mr Fairbrother recalled how Dunne was in great form, even remarking that the party was "going to last three days".
Yesterday's arrests bring to nine the amount of people arrested by gardai investigating 'The Don's' murder.