A 33 year old man has been arrested in Newtownabbey this evening in connection with the murder of John Boreland.
The prominent loyalist was gunned down outside his home in Sunningdale Gardens on August 7.
The 46 year old father was shot a number of times as he got out of his car to walk to his flat. He died at the scene.
Three other men arrested earlier today remain in custody.
A 29 year old was arrested in Ayrshire in Scotland this morning whilst a 33 and 61 year old were detained in Belfast.
They're all being taken to Musgrave Police Station for questioning.
The officer leading the investigation, Detective Chief Inspector Justyn Galloway from PSNI Serious Crime Branch, said: “Officers have travelled to Scotland to assist colleagues from Police Scotland with the arrest and related searches."
Police are continuing to appeal for information about a silver Renault Megane car thought to be used by the killers.
"The car, registration number GJZ 4870, was in the Ballysillan area of north Belfast in the days leading up to the murder" DCI Justyn Galloway added.
“We are still very keen to hear from anyone who saw it, saw who was in it and where it had been parked. We are re-issuing two photos of a similar vehicle to enhance our appeal.
“We are also interested in talking to anyone who saw the Megane between the Sunday night of the shooting and when it was found partially burnt out at the old quarry on Wheelers Road near Lisburn on the morning of Tuesday 9 August.
“The car has been the subject of a detailed forensic examination and I would ask anyone with information about the vehicle to contact detectives on the non-emergency number 101 or use the independent charity Crimestoppers 0800 555 111 where they can provide information anonymously.”
One man was arrested in Belfast in the immediate aftermath of the murder but later released unconditionally.
Previously, a number of searches were carried out in Belfast and a vehicle was seized.