Four people are now being questioned by detectives about the killing of 19-year-old Peter McNally in Craigavon.
He was shot in a house at West Acres at Drumgor early on Monday morning.
Two men, aged 47 and 27 were arrested on Monday after the murder. The other two people were arrested on Wednesday.
Meanwhile, police have said they are no longer treating as suspicious the death of a 33-year-old woman at Drumgore in Craigavon.
Georgina Gibson was in the house at West Acres in which Mr McNally was murdered.
Her body was found in the house at 0400 BST on Wednesday.
A post mortem examination has taken place and detectives said they were not seeking anyone in connection with her death.
The police said they have also recovered a revolver and a pistol at a vacant house at Drumellan Gardens.
The weapons were discovered hidden in the back garden.
Detectives believe Mr McNally, who had no fixed home, may have been the victim of a dispute between criminals.
It is understood he was on the run from Hydebank Young Offenders' Centre in Belfast.