Three men aged 49, 32 and 28 and a 28-year-old woman were arrested in the city on Saturday evening.
The victim was found in his living room at a house on Coulson Avenue in Lisburn at about 8,45 pm on Friday.
The PSNI carried out two searches and a number of items were taken away to be examined.
Det Ch Insp Eamonn Corrigan from MIT said the PSNI’s investigation was “at a very early stage” and he appealed for information.
“A post-mortem examination will be carried out in due course to determine the cause of his death,” he added.