The man shot dead outside his north Belfast home had survived a previous murder bid six-and-a-half years ago.
The scene of the murder in north Belfast
Loyalist sources said Stephen Paul, 28, had links to the paramilitary group, the Loyalist Volunteer Force.
He was shot at Wheatfield Crescent, Crumlin Road, on Saturday at about 1740 BST. Another man was injured.
The murder has been linked to the continuing feud between loyalist paramilitaries, the Ulster Volunteer Force and the LVF.
The police said a connection "with ongoing tensions within loyalism is one active line of inquiry".
The victim's uncle, William Paul, known as Wassy, was shot dead at his home in Bangor's Kilcooley estate in July 1998. He was a drug dealer with loyalist connections.
Stephen Paul lived in the same estate. In January 1999, he was ambushed outside his house. He managed to stagger to a main road to get help and underwent emergency surgery.
It is understood that he had served a number of jail terms, including one for seriously assaulting his partner.
Security sources said he was involved in criminality, particularly in drug dealing.
He had received numerous death threats over the years and had moved house on several occasions.
It is the third killing in the feud between rival loyalist paramilitaries.
The police said their investigation was at an early stage.
On Sunday, police conducted searches of the scene of the murder.
Officers in white forensic suits searched the area around Wheatfield Crescent.
Earlier, police officers and soldiers were also stationed at Belfast's Mater Hospital.
The other man injured remains in hospital, but his injuries are not thought to be life threatening.
'End violence now'
BBC Ireland correspondent Denis Murray said it was not clear whether the Ulster Volunteer Force or another loyalist group carried out the killing.
NI Secretary Peter Hain has condemned the murder.
Mr Hain said he was discussing the situation with Chief Constable Sir Hugh Orde.
"This is a grisly murder of a mafia kind - gangsterism masquerading as loyalism," said Mr Hain.
"It has to stop - it is intolerable. I will be talking to the chief constable about stopping it.
"We have got to root out this mob violence and gangsterism from loyalist communities which have suffered so much."
SDLP Belfast deputy lord mayor Pat Convery said it was clear the loyalist feud was "spiralling out of control".
"Each death is a tragedy leaving a family to grieve and the community to suffer," he said.
Chief Superintendent Mike Little, head of the police's North Belfast District Command Unit, described the killing as a "senseless attack".
The police are appealing for information about a small blue car that may have been used by the killers.
The vehicle was found burnt out in the nearby Forthriver estate.
It is understood a blue Vauxhaul Astra, RDZ 5600, was involved in shooting and police are keen to trace the whereabouts of the car before and after shooting.
They believe two people may have been in the car.