A man was shot dead in front of his young son in the car park of a busy supermarket, police said.
A lone gunman shot the 35-year-old father several times as he targeted him among crowds of shoppers outside the Sainsbury's superstore on the outskirts of Bangor, Co Down.
The PSNI said it was lucky the youngster was not killed or seriously injured as well.
There were reports of a confrontation before the killer fired four to six bullets at his victim.
The victim was targeted next to a black SUV type vehicle on the edge of the supermarket car park and detectives believe that there may have been more than 100 witnesses to the shooting and the aftermath.
Superintendent Brian Kee, District Commander Ards and North Down District, described the murder as brutal, senseless and horrendous and warned of the psychological trauma the man's son has suffered.
"This cold blooded murder was carried out in broad daylight in front of families who were out enjoying this Bank Holiday weekend," he 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. This young boy witnessed everything and he will undoubtedly carry that memory for the rest of his life. We are very lucky that we are not also dealing with the death of this child today."
It is understood the incident occurred at about 3pm in the packed car park of the supermarket just off the Balloo Link road.
The victim was wearing shorts and trainers.
After he was shot he could be seen lying on his back next to the vehicle which had been parked at the edge of the car park near the main road.
The front left passenger door of the car lay open while he was treated by a team of paramedics.
One eyewitness said medics worked on him for 45 minutes before he was transferred to an ambulance and driven slowly from the scene under a police escort.
Mr Kee said the gunman showed total disregard for the safety of the public, including other children, who were in the car park.
And he appealed for anyone who was in the car park to make contact with the detective unit in the coming days.
"We are keen to gather as much information as possible," Mr Kee said.
"At the centre of all of this we have a grieving family and local residents coming to terms with a brutal shooting in the heart of their community."
Management at the Sainsbury's shut the door to the store after the incident.
Mr Kee said local police supported by specialist officers will maintain a presence in the area around Balloo Link to reassure people living in the area.
"We all have a part to play to ensure that the community in Bangor has the time to come to terms with what has happened here and to ensure that those responsible for this murder are brought to justice," he said.
Steven Agnew, Stormont MLA for North Down, lives about two miles from the scene of the shooting.
"It's very shocking that 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."
Alan Chambers, Ulster Unionist MLA in Stormont, said he was on the scene 10 minutes after the attack.
"It was clear to me that we could easily have been dealing with a lot more casualties due to the nature of the attack in which the victim was hit a number of times," he said.
Northern Ireland Secretary of State James Brokenshire added his condemnation.
"Deeply disturbed by news of the shooting in the Sainsbury's car park in Bangor. Brutal act of violence that has no place in Northern Ireland," he said on Twitter.
Alliance North Down MLA Stephen Farry said the killing "sent shockwaves" through the town.
"This was a brutal incident, made all the more reckless and shocking by the fact it took place in a busy supermarket car park on a Sunday afternoon. Shoppers going about their regular business could have easily been on the end of this attack," he said.
Mr Brokenshire later urged anyone with information to go to the police
"The community in Bangor and all those involved will understandably be deeply shocked by this horrendous murder," he said.
"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.
"PSNI are doing all they can to bring to justice anyone involved. Help them, anonymously if need be, through Crimestoppers by giving information. There is no place for this in Northern Ireland."