The man, whose body was found in Lurgan yesterday, has been named locally as Marcell ‘Junior’ Seeley.
Police are treating Mr Seeley’s death as ‘suspicious’.
His body was found in the Dingwell Park flats in Taghnevan around noon yesterday.
It is understood Mr Seeley, who was aged just 33, was discovered with head injuries.
A spokesperson for the NI Ambulance Service said it received a call just after noon on Tuesday.
“A Rapid Response paramedic and Accident and Emergency Crew were at the scene within seven minutes however the patient was deceased,” he said.
A PSNI spokesperson said: “The death is being treated as suspicious and a post-mortem examination will take place to determine the cause.”
Detective Chief Inspector Eamonn Corrigan, who is leading the enquiry, said: “If anyone saw anything unusual in the Dingwell Park area in recent days, we would like them to contact detectives at Mahon Road police station by calling 101.
Sinn Féin MLA John O Dowd said: “This is a tragic event and it is still early in the police investigation on the circumstances. Our thoughts must be with the family and friends of those affected. Everyone in the Taghnevan and wider community will be shocked by this death. ”
Police forensic teams were last night scouring the flat for clues.