Paul McNally, 26, was shot as he left Sean Graham's bookmakers at the junction of Brompton Park and Crumlin Road. He died in hospital two days later.
Police believe two gunmen opened fire in a random sectarian attack on a group of men, on 5 June 1976 at around 2.40pm. Mr McNally and another man suffered serious injuries.
The victim, who worked as a plumber, was married and had a four-year-old daughter and a five-month-old son.
A passing army patrol opened fire on his killers as they fled the scene in a yellow Ford Cortina, which had been hijacked in the Shankill Road area before the attack.
On Monday, a man was detained by officers from the PSNI Serious Crime Branch in Belfast after the inquiry was re-opened due to new information being received.
He was released pending a report to the Public Prosecution Service.
"Inquiries by Detectives from Serious Crime Branch are continuing," a police spokesperson said.