VICTIM shot 15 times as he sat in his caravan.
"He would have been able to pay back the money if he had got cash back from the people who owe him money, but time just ran out for him."
McDonagh was known to gardai but had no convictions for serious criminal offences.
It is understood that he dealed in selling scrap but had become involved with the ruthless Finglas gang -- one of the most feared in Ireland.
This mob are also the chief suspects for shooting another Traveller -- Anthony 'The Mole' McDonagh -- in a northside criminal dispute on July 15 last year.
In the latest murder, the killers struck just before 10pm on Saturday when Tom McDonagh was alone in the mobile home where he lived on the St Margaret's halting site off St Margaret's Road, near the Ikea store, in Ballymun.
The dead man's wife Kate was away for the weekend and his three adult children, one of whom lives in the caravan next door, were not at their parents home when the attack occurred.
Heartbroken Kate said: "I never leave the house but they wanted to get me away for a few days. If they hadn't I would have been there. I'm numb. I still can't take it in," she said.
On Saturday night, the two attackers drove into the back of the cul de sac site of about 60 caravans.
They reversed their car into McDonagh's bay, got out of the vehicle and went to the victim's mobile home where they opened fire through the front door after knocking on it to get their target to come to the door.
At least one of the attackers is then believed to have gone into the caravan and shot the victim again to make sure he was dead.
Today, the scene of the fatal shooting remained sealed-off be gardai.
Forensic units have placed coloured rods through the bullet holes in the mobile home to determine the trajectory of the shots and the standing position of the gunman.
The shots are also numbered.
One of the bullets went through the home and out the back of it, before breaking a perspex window in an unoccupied caravan parked in a neighbouring bay at the halting site.
Neighbours said they did not believe Tom McDonagh owed any money to gangs.
"He was a quiet lad, they used to call him the quiet man around here. It's a terrible shock," said a woman who lives nearby. After the shooting the gunman was driven away by his accomplice.
Their vehicle went back out onto St Margaret's Road and turned left towards Finglas.
About one kilometre up the road they turned right into the Mayeston Lawn apartment block, parked their stolen black Nissan Qashqai in a parking bay and set it on fire.
The men then ran through bushes beside the apartment block and scaled a fence, which brought them on to the side of the southbound carriage of the M50.
Gardai believe it was at this spot, about 200m before the exit for Finglas, that the attackers were collected and driven from the area.
Officers have appealed for drivers, who were near the Finglas exit between 9.45pm and 10pm last Saturday, to contact them on 01 6664400.