Police are now treating the death of a security guard in Henderson in West Auckland a week ago as a homicide.
The body of Charanpreet Dhaliwal, 22, was found by his colleagues at a construction site near Lincoln Road and the North Western Motorway.
Police were treating the death as unexplained but now say Mr Dhaliwal died of head injuries after being assaulted.
They are reviewing all available security surveillance footage in the area.
Police want to identify several people who are known to have been in the area at the time and want anyone with information to contact them.