Detectives investigating the murder of Stephen Carson have arrested three men.
28-year-old Stephen Carson was shot dead in his house at Walmer Street in south Belfast on Thursday night as his 26-year-old partner and son watched on.
The nine-year-old boy has been left traumatised.
Police were hunting four men involved in the killing - and arrested three, aged 32, 37 and 39 on suspicion of murder following searches in west Belfast on Friday evening.
A firearm was recovered and has been sent for forensic tests while the men remain in custody.
Mr Carson, who moved into the area following his recent release from prison, and was originally from Turf Lodge in west Belfast.
The family were eating a meal at around 10.45pm when the gang burst in.
A confrontation followed and Mr Carson took cover in a downstairs bathroom.
However, the gang shot him through the door.
The police officer leading the hunt for the murder gang, Detective Sergeant Kevin Geddes, called the slaying "cold blooded and brutal" and has appealed for witnesses.
Mr Geddes said: "At approximately 10.45pm Stephen was sitting in his home at 77 Walmer Street with his partner and his nine-year-old son. As they were enjoying a takeaway meal at least three men carrying a hammer and a shotgun burst in and there was a confrontation.
"Stephen ran into the downstairs bathroom but the shotgun was fired through the door and Stephen sustained a head injury which proved to be fatal.
"His 26-year-old partner and his nine-year-old son were left in the house as the killers made their escape on foot in the direction of Haywood Avenue.
"A fourth man may have been outside the house during the murder.
"His partner and son were not physically injured but have been severely traumatised."
A local woman said: "I can't believe it. I walk past here every day on way to my daughter's house.
"I passed the house just about 10.30pm on Thursday night but didn't see or hear anything.
"I am totally shocked by what has happened."
As part of their investigations police searched a house on Sunnyside Street yesterday morning, only a few hundred metres from the scene of the murder.
A number of individuals were seen leaving the house, including women and children, but police confirmed no arrests were made.
A police helicopter hovered over the area for most of yesterday morning and police remained at the house on Sunnyside Street for most of the evening.
Mr Geddes added: "Our main line of enquiry, but not our only line of enquiry, is that Stephen was shot as part of a criminal feud. We do not believe at this stage there was any paramilitary involvement, nor do we believe this was sectarian.
"I have a number of appeals. I want to hear from anyone who was in the area of Walmer Street and Kimberly Street around 10.45pm on Friday night or from anyone who saw three or four men in that area around that time.
"I also want to hear from anyone who saw any suspicious or strange behaviour at or near 77 Walmer Street.
"We are also looking for the occupants of a silver taxi, possibly a Mercedes, which was in Walmer Street at the time of the incident around 10.45pm.
"This was a cold-blooded and brutal murder. These are not convenient labels to describe what happened last night. They are an honest opinion about the horrific events which took place in 77 Walmer Street. It is vital that Stephen Carson's killers are caught and brought before the courts."
A number of politicians expressed their anger at the shooting.
South Belfast SDLP MLA Claire Hanna said: "I want to condemn in the strongest possible terms this vicious murder. There has never been any place for this kind of shocking violence on the streets of our city.
"I've been to the scene on Walmer Street, where an entire community is absolutely in shock.
"This is a well-integrated area with families, young workers and new communities all living together in peace.
"It's extremely worrying that someone who would seek to hurt others like this has access to guns and is willing to commit such a violent act."
Local UUP MLA Michael McGimpsey said: "Once again people have woken up to the shocking news that a man has been murdered at his home by an armed gang.
"There is simply no excuse that can justify this brutal and callous killing.
"Northern Ireland was plagued with this type of incident for decades and nobody, but nobody, wants to return to those dreadful days."
Deputy First Minister Martin McGuinness described the murder as a "terrible tragedy".
He passed on his sympathies to the victim's family and urged anyone with information to pass it to police.
Detectives are investigating a possible link between this murder and the murder of pizza delivery driver Kevin McManus in west Belfast almost three years ago.