The man shot dead in front of his son in a supermarket car park in County Down on Sunday has been named locally as Colin Horner.
He was a friend of loyalist Geordie Gilmore who was shot as part of a paramilitary feud in March.
Mr Horner, 35, was murdered in a Sainsbury’s car park at Balloo Link, Bangor, at about 15:00 BST on Sunday.
Police said it was a “brutal, senseless and horrendous” attack that his son will carry with him throughout life.
Car park murder victim shot in front of son
High-profile loyalist George Gilmore dies after shooting
It is understood Mr Horner was approached by a lone gunman and there are reports of a confrontation before the killer fired four to six bullets at him.
PSNI Supt Brian Kee said: “The recklessness of this murder is all too evident. It is beyond belief that the gunman shot the victim when he was out with his son.
“We are very lucky that we are not also dealing with the death of this child today.”
He said the gunman also showed “total disregard” for the safety of the public, including other children, who were in the car park at the time of the attack.
Police have appealed for witnesses.
Ulster Unionist North Down MLA Alan Chambers who arrived at the car park about 10 minutes after the shooting said the scene was “surreal”.
“There was a casualty on the ground, there was about six paramedics round the person working very, very hard with CPR and also administering fluids to him,” he said.
“They worked on him for maybe 45 minutes, they put him then onto a trolley and moved him into an ambulance and worked on him in the ambulance for another 20 minutes and then the ambulance left the scene with a police escort.”
Mr Chambers said hundreds of people were there, unaware of what had happened.
“On a sunny bank holiday weekend, as a man lay fighting for his life, people were walking by blissfully unaware of what happened carrying tins of paint and wallpaper under their arms,” he said.
Northern Ireland Secretary James Brokenshire said the Bangor community would be “deeply shocked” by this murder.
“To shoot someone in a busy supermarket car park in sight of children and shoppers shows a brutality and recklessness that will not be tolerated,” he said.
“The PSNI are doing all they can to bring to justice anyone involved.”
DUP MLA Gordon Dunne said people were in “shock and disbelief” at what had happened.
“This was something we thought was past us, but, sadly, on occasions, is still with us,” he told BBC Northern Ireland’s Good Morning Ulster.
Mr Dunne said any suggestion of a link to a loyalist feud was “speculation”.
“Whoever is responsible must be brought before the courts for this terrible deed,” he said.
The DUP MLA said community relations were extremely good in Bangor and, as he and his colleagues were canvassing for the forthcoming election, they had a sense that things were “stable and settled”.
Alliance North Down MLA Stephen Farry said the shooting had “sent shockwaves” throughout the town.
“My thoughts are with the loved ones of the man shot dead. There can never be any excuse for carrying out such an act, which has left a man dead and a family mourning,” he said.
“Violence has no place in our society and those who carried out this attack must be taken off the streets. I would urge anyone with information on it to contact police immediately.”
Sinn Féin MLA Chris Hazzard condemned the shooting.
“Whoever was behind this shooting wants to drag us back to the past. It will not happen,” he said.
Green Party MLA Steven Agnew said the murder was “very shocking”.
“This took place in broad daylight on a busy shopping day, with children and families present. A large number of people will have been shocked by this incident. Anyone who has witnessed or was nearby, undoubtedly, this will live long in their memory.”