Loyalists are suspected of murdering a man after getting his young son to send him to the front door of his Co Down home.
They are also being blamed for a gun and petrol bomb attack on a house in north Belfast and the shooting of a teenager in west Belfast.
Mr Mark Apsley (38) died in a hail of bullets when a lone gunman called at his house in Dickson Park in the village of Ballygowan on Saturday evening.
Police said they were trying to establish a motive for the brutal slaying but said the killing of the Protestant father-of-two was not thought to be sectarian.
They were understood to be investigating claims the killing was linked to a personal dispute between Mr Apsley and an east Belfast Ulster Defence Association boss.
Mr Apsley had only moved into the house on an estate in the small village of Ballygowan a month ago.
The victim's five-year-old son answered a knock at the front door to a man who asked him to get his father, police said.
As Mr Apsley arrived at the door the gunman opened fire at point blank range, pumping five or six shots into his victim who died instantly.
His young son did not witness the killing, he had returned to the living room where his mother was sitting with his 18-month-old sister.
Chief Inspector David Green condemned the killing, but expressed relief that the little boy did not witness his father's death. But he added: "Children this time of year should be looking forward to Santa, presents and Christmas, not to have such an appalling murder on their minds."
Local Democratic Unionist Party councillor Mr Jack Beattie expressed his horror at the murder. "It really saddens me to see this sort of thing, especially as we come towards Christmas."
Loyalists are also being blamed for a gun and petrol bomb attack on a house in north Belfast early today.
One of two petrol bombs set a car and caravan on fire outside the house in Westland Drive and there were reports of shots being fired as the attackers sped off in a car.
Mr Sam Duddy, chairman of the Ulster Political Research Group, blamed loyalists from the Shankill Road area of west Belfast for the attack. He said the family in the house were the victims of "continual harassment" and had only moved to the house two weeks ago after being forced to flee another home nearer the Shankill.
Meanwhile an 18-year-old man is being treated in hospital after being shot in both legs in a paramilitary style attack in Shankill Road area.
He was in the kitchen of a house in Crimea Street when three masked men smashed in the front door and attacked him, said police.
One of the men was armed with a handgun and shot the victim in both thighs, the others battered him with iron bars, breaking at least one limb.
In Co Armagh police are investigating a gun attack on a house in the village of Lawrencetown during which shots were fired through the living room and bedroom windows of a bungalow.
Four people sleeping in the house at the time of the early morning attack escaped injury.
Police said the shooting was not believed to have a sectarian motive.