Father-of-two Stephen Carson was shot in the head through a bathroom door with his partner and nine-year-old son just yards away in another room.
The 28-year-old, who was released from prison last October having served a sentence for robbery, was murdered when three men armed with a hammer and shotgun forced their way into a house in the Ormeau Road area of south Belfast on Thursday night.
After a confrontation the victim ran to a downstairs bathroom, but was shot through the door.
The men made off on foot, with police believing a fourth man was waiting outside the property at Walmer Street keeping watch.
Mr Carson was forced to leave his native west Belfast following a bloody street brawl in Turf Lodge in 2010 involving a large number of men, which saw a man almost lose an arm in a samurai sword attack.
His close friend Kieran McManus, who was convicted of affray, was shot dead in 2013.
The deliver driver was targeted outside a Domino's Pizza branch on Kennedy Way in west Belfast.
He had been forced to flee Turf Lodge and had been living in Crumlin village in Co Antrim at the time of his murder.
The attack was claimed by the Continuity IRA, but was thought to have involved criminals previously expelled from other republican groupings.
Following the murder a member of Mr McManus's family received death threats.
Mr Carson had also received threats, the most recent from a group claiming to represent the INLA, although this was denied by a spokesperson for the republican group which is officially on ceasefire.
Instead sources say members of a gang made up of people who have been thrown out of other groups are behind the shooting.
They are also involved in tiger kidnap and cash-in-transit robberies and have been blackmailing drug dealers into handing over large sums of money.
Mr Carson's mother told the Irish News yesterday she was still too shocked to speak about the murder of her son.
Police investigating the killing, which happened at around 10.45pm on Thursday, carried out a search of a house in nearby Sunnyside Street yesterday and removed items for examination.
Detective Superintendent Kevin Geddes said Mr Carson was known to police but had been trying to get his life together.
“Our main line of enquiry, but not our only line of enquiry, is that Stephen was shot as part of a criminal feud.
"We do not believe at this stage there was any paramilitary involvement nor do we believe this was sectarian."
He added: "This was a cold-blooded and brutal murder. These are not convenient labels to describe what happened last night. They are an honest opinion about the horrific events which took place in 77 Walmer Street. It is vital that Stephen Carson's killers are caught and brought before the courts."
Mr Geddes said Mr Carson's partner and child had been left severely traumatised.
"If you think of a nine-year-old boy who had to see and listen to his dad being killed," he said.
SDLP MLA Claire Hanna said the entire community at Walmer Street was in shock.
"This is a well-integrated area with families, young workers and new communities all living together in peace. No one could ever have anticipated that we’d be waking up to something like this."
Sinn Fein councillor Deirdre Hargey said the killing was "wrong and I condemn it utterly".
DUP MLA Emma Pengelly also said such "cold-blooded brutality is truly chilling", while Ulster Unionist Michael McGimpsey called on the entire community to assist police to find the killers.
