Police have launched a homicide inquiry after the body of an inmate was discovered at Auckland Prison on Sunday.
Samoan-born Tue Faavae, 23, was serving five years for aggravated robbery. He was found dead inside a sector of the East Wing about 11am.
A post-mortem on Monday revealed that Faava died as a result of injuries suffered in a serious assault by other inmates.
Detective Senior Sergeant Kim Libby says police are concentrating on activities in the wing before the discovery of Faavae's body.
About 20 officers are working on the investigation.
The death comes less than a month after convicted killer Antonie Dixon was found dead in his cell, renewing concerns about security in prisons.
Auckland Prison is New Zealand's only maximum security facility.
Department of Corrections chief executive Barry Matthews says the old design of Auckland Prison means it is not possible for guards to have inmates in sight all the time.
Mr Matthews told Checkpoint six prisoners are allowed out of their cells at one time and there was no indication before they were unlocked of any adversity between the inmates.
He cannot say if Faavae was attacked by more than one inmate.
Police, the Prison Inspectorate, the Office of the Ombudsmen and the Coroner are investigating the death.
Mr Matthews has asked the Prison Inspectorate investigation to include reporting back on whether the proper standards, procedures and operational systems were in place and being complied with.
Listen to Checkpoint item