“This has the characteristics of a professional hit, which is common in cases involving organised crime”
Sean Fox was gunned down by two masked men in Donegal Celtic Football Club on the Suffolk Road on Sunday.
Police said the two gunmen fired 20 bullets at Mr Fox (42) and stood over him as he collapsed.
Detectives said they are following several lines of inquiry, including Mr Fox’s friendship with another murder victim Jim Donegan, who was shot dead outside a school in Belfast in December 2018.
Former Assistant Chief Constable Alan McQuillan said the killers showed a chilling level of organisation.
He said the murder was “a very well-organised incident — they knew exactly where [Mr Fox] would be and what time he would be there, and they were able to walk into the venue with ease and carry out the murder.”
Mr Fox was a member of the so-called ‘Marbella Crew’ of high-profile drug dealers.
He publicly denied he was a major player in the drugs trade following the death of Mr Donegan, a fellow Marbella Crew member and close friend.
Mr McQuillan added: “The main difference between the average murder and a drug-related murder is that the average murder is local.
“This has the characteristics of a professional hit, which is common in cases involving organised crime.”
When asked about how long a case of this calibre could take to solve, Mr McQuillan said: “The police are in it for the long-haul.
"They will treat it as a pattern with other organised crimes in the area and will probably see if there are any links with drug-dealers in the Irish Republic.
“It could be an instance where there was a dispute or that the gangs were fighting for territory.”
Mr Fox was shot multiple times by two gunmen in front of his uncle and one of his two children while he watched a football match.
The fatal attack lasted 21 seconds, police said this week.
On Tuesday, CCTV was released showing the gunmen, who were masked, enter the premises before fleeing the scene after shooting Mr Fox.
Detective Superintendent Eamonn Corrigan described the incident as “a calculated, planned, ruthless execution”.
He continued “The gunmen arrived, carried out the murder and left the club in under a minute. It was carried out in broad daylight and in the presence of others.”
Police are following several lines of inquiry, specifically Mr Fox’s relationship with Mr Donegan, who was killed in his £80,000 Porsche outside a school in west Belfast in 2018.
It is believed that the Marbella Crew held a summit to try and establish who is giving information on their activities to republican hitmen.
Donegal Celtic Sports & Social Club have since paid tribute to staff following the murder of Mr Fox.
Writing on their Facebook page, the club expressed their “sincere condolences to the Fox family at this very sad time after the passing of our member Sean.”
The club added: “Our thoughts are also with our staff, members and guests who were present at the time.”