The victim was was stabbed to death at a house in Castlereagh Place in east Belfast on Saturday evening around 10 pm.
Three people – two men, aged 21 and 25, and a 25-year-old woman – were arrested a short after the stabbing on suspicion of murder.
In follow up inquiries on Sunday, MIT detectives arrested a third man aged 31.
Police said they were following a definite line of inquiry and have appealed for information about the attack.
Neighbours described the couple who live at the house as quiet and private people who have lived there for many years.
It is understood that family members were visiting when the stabbing happened.
Emergency services tried to resuscitate the man on the pavement outside the house but he died a short time later.
Detective Chief Inspector Alan Dickson, of the Major Investigation Team: “I appeal to anyone who was in the Castlereagh Place area around 10 pm on Saturday night and witnessed the incident or has any information to contact Detectives at Ladas Drive on the non-emergency number 101
“Or, if someone would prefer to provide information without giving their details, they can contact the independent charity crimestoppers on 0800 555 111.