Gardai have arrested a 22-year-old man in connection with the murder of Edward O'Connor in Finglas yesterday.
The chief suspect was arrested in the Finglas area around noon today. He is being held at Blanchardstown garda statioin.
A pub row led to the father being shot dead in front of his two sons, gardai believe.
The victim of Dublin's latest gun murder, Edward O'Connor, was shot three times in the back. He was gunned down as he walked away from a group of men having agreed to put their differences aside.
The horrific attack happened on Ballycoolin Road in Finglas at 5pm yesterday.
Gardai had launched a manhunt for the killer who is understood to have been involved in an earlier fist fight with Mr O'Connor's son Darren.
The Irish Independent understands that the dead man had been involved in a long-running feud, which stemmed from an incident in which Edward O'Connor had been accused of abusing a young woman.
However, following a garda investigation, the Director of Public Prosecution (DPP) decided there was insufficient evidence with which to charge him.
Gardai are continuing to hold a woman and her boyfriend in garda custody.
Sources revealed the shooting was connected to a fight which took place in a Finglas pub on Saturday night between Darren O'Connor and another man.
Darren was seriously assaulted during the row and part of his ear had been bitten off. Sources said that Edward O'Connor, accompanied by his sons Darren and Eugene and his two brothers, met the man who was involved in the pub attack for a "straightener" to sort out their differences.
It is understood the two men had a fist fight and had then shaken hands. The O'Connors were walking away when another man who was present produced a hand gun and shot the victim three times in the back.
The killer then fled the scene with the man who had assaulted Darren O'Connor.
Paramedics worked to save Mr O'Connor at the scene but he was pronounced dead in James Connolly Memorial Hospital in Blanchardstown an hour later.
Last night sources revealed that gardai were following a "definite line of enquiry" after the suspect was identified by Mr O'Connor's family members.
A source said: "The victim and his family members had shaken hands with the other individuals present and were walking away when a man produced a gun and shot him in the back without warning.
"This was a particularly callous, cold-blooded murder. The victim and his family members clearly didn't expect any further trouble and, believing that they had sorted their differences, had turned to walk away."
The source added: "The murder was witnessed by Mr O'Connor's sons and brothers and gardai are following a definite line of enquiry. The victim's family members are extremely distraught."
Local Sinn Fein councillor Anthony Connaghan said the shooting occurred at "O'Connor's yard" adding "it's a scrap yard there just up past Cappagh Hospital".
"It's just loads of cars basically and there's a bit of land at the back of it and a couple of containers," he told the Irish Independent.
Paul Williams, Ken Foy and Sam Griffin