A senior paramilitary murdered with a shotgun outside his Belfast home was the victim of loyalist in-fighting, detectives believe.
The officer leading the investigation into the murder of prominent Ulster Defence Association (UDA) member John Boreland said main lines of inquiry focused on "tensions within loyalist groupings".
Police are stepping up patrols in the north Belfast area where Sunday's shooting happened amid fears of retaliation attacks.
Police Service of Northern Ireland (PSNI) Detective Chief Inspector Justyn Galloway said the 46-year-old father-of-three, who survived a murder bid in 2014, had been made aware of a fresh threat to his life in recent months.
The known criminal was shot a number of times as he got out of his car outside his flat in Sunningdale Gardens in the unionist Ballysillan area at around 9.50pm on Sunday.
"It is my early assessment that he was shot with a shotgun," said Mr Galloway.
"John was known to police. He had been the victim of a previous shooting in 2014 and he was aware that he was under threat at the time of his murder."
Mr Boreland, who was engaged to be married, had taken steps to "counter" the threat, Mr Galloway said.
The detective said the shooting involved an element of planning, but he would not be drawn on whether he believed the killing was carried out by fellow UDA members or other loyalist paramilitary groups.
He did rule out a sectarian motive.
"Our main lines of inquiry are centred around loyalists and tensions within loyalist groups and the loyalist community, that is as far as I am prepared to say at this stage."
Mr Galloway said Mr Boreland's family had been left "devastated".
Superintendent Paula Hilman said police would be stepping up patrols. She appealed for calm and warned against anyone taking the law into their own hands.
"We are aware of tensions within the loyalist community in north Belfast and we already have a significant police operation across north Belfast and that will continue over the coming days," she said.
Police have appealed for anyone who was in the Sunningdale Gardens area at the time of the shooting to come forward.
They are also keen to speak to anyone who spent time with Mr Boreland on Sunday and also his wider circle of friends and associates.
Detectives have made a direct appeal for help tracing the drivers of three vehicles seen leaving in the area - a motorbike, a silver Renault Megane and a black Peugeot 307.
In August 2014, Mr Boreland, who was heavily linked with local criminality, was shot in the thigh by rival loyalists.
There have been mounting tensions between loyalist groupings in north Belfast in recent weeks.
Loyalist gunmen have been responsible for dozens of murders since the organisations supposedly went on ceasefire in the 1990s. Many killings have been linked to feuds and turf wars among loyalist rivals.
The latest shooting has prompted further questions about the authenticity of the ceasefires.
Last year, the main loyalist paramilitary groups restated their commitment to non-violence as they came together to launch a new initiative - the Loyalist Communities Council.
Mr Boreland was a close associate of well-known north Belfast loyalist Andre Shoukri.
Ten years ago the UDA expelled Mr Shoukri and his late brother Ihab from the organisation after a bitter fallout between their gang and the mainstream leadership.
First Minister Arlene Foster, Deputy First Minister Martin McGuinness and Northern Ireland Secretary James Brokenshire are among many politicians to condemn the killing of Mr Boreland.