Detectives are investigating reports that Gary Hutch was shot dead on the orders of his own gang, the Christy Kinahan drugs trafficking cartel, after he became embroiled in a cash dispute with the mob.
Sources say that Hutch was a key figure in the gang up until less than a year ago but had a major falling out with the cartel and that he knew that he was a marked man in recent months.
One prominent theory is that the dispute centred on a €2m shipment of cocaine destined for the British market that went missing last year.
It is understood that family members of the victim had been approached in Dublin recently by a thug demanding a six-figure sum of money which he claimed Hutch owed.
The family had been "living in dread" of getting bad news.
In Spain, just 24 hours after the daylight hit, a few shreds of crime scene tape and bullet-pocked walls were the only reminder of the horror that unfolded at the quiet Angel de Miraflores complex on Spain's Costa del Sol, near Marbella.
It has emerged that the hitman fired eight bullets at the 34 year-old shortly before mid-day on Thursday as he fled for his life. At least four hit him in the back, chest and head.
Hutch died at the scene in front of horrified pensioners who have retired to live in the sun.
His killer calmly walked past security cameras and through an electronic gate to a waiting getaway car which was later found torched.
A bullet hole in the wall was a stark reminder of what had happened.
However, no police were carrying out door-to-door inquiries and no appeals were being made about the brutal killers. The grounds had been cleaned and returned to normal.
Just last month police in Spain officially closed the investigation into the murder of drug dealer Gerard 'Hatchet' Kavanagh.
Gary Hutch's remains are still in Spain and his father Patsy, a carpet fitter, is expected to make the heart-breaking journey over the coming days to bring his son home.
The Miraflores resort lies between the towns of Fuengirola and Marbella, just off the N340 dual carriageway which runs along the Costa del Sol and very near to missing Amy Fitzpatrick's mum Audrey's old home.
Neighbours say that they rarely saw or heard from him. In fact many didn't even realise that he was living in a ground floor apartment.
"I thought his name was Finnegan," one woman said yesterday. "I knew he was Irish but I didn't even know his first name. He was in that apartment but we thought it belonged to a relative of his and that he had been in Ibiza or something."
Another neighbour, who asked not to be named, said: "We heard the first shots go off in the garage under our home and then saw this man running around the garden where the swimming pool is with a balaclava on and gloves.
"We thought at first it was a terrorist. There were lots of shots, around a dozen, and then we saw him running away."
It is understood Hutch, a convicted criminal, was trying to escape out of a back exit on the gated estate where he lived when he was cornered and shot in the head and chest.
The killer has been described as a tall strong man dressed in jeans and a black tracksuit top.