The PSNI has launched a murder investigation into the death of 41-year-old Matthew Goddard following the results of the postmortem.
Police said Goddard was killed in a "sustained and brutal attack" and had been beaten with his electric guitar and other objects.
A 12-year-old boy was arrested along with a 17-year-old following searches on Sunday. The 12-year-old boy has been released on bail pending further inquiries.
A man (21) and woman (24) were arrested on Saturday are still being questioned over the murder.
Police told the BBC they were "not prepared to disclose the exact cause of death at this stage."
Detective Chief Inspector John McVea added: "Mr Goddard suffered a brutal and violent attack in the living-room of his home, a place where he should have felt safe.
"Mr Goddard was not previously known to police.
"We believe he may have been involved in drugs and this is one of a number of lines of inquiry police are investigating.
"At this stage, we do not know the reason why Mr Goddard was attacked, but this type of vicious behavior has no place in society."