The inmate found dead in his Mt Eden prison cell had admitted violence and sex charges against women and children spanning a period of four decades.
The prisoner was Liberty Charles Baker, 63, who was due to be sentenced in the High Court at Whangarei on Wednesday after pleading guilty to nearly 80 charges including rape, sexual violation, assault, kidnapping, threatening to kill and grievous bodily harm.
His sentencing was delayed until December but now detectives from Auckland City are investigating the "sudden death" of the remand prisoner after being notified by phone at 8.41am yesterday.
A post-mortem examination is scheduled for today and the death was referred to the Coroner, as well as subject to a review by the Corrections Inspector.
Key questions will focus on the circumstances leading to his death including whether he was threatened by other inmates and if there was sufficient supervision of Baker by prison staff.
It is understood Baker's body was moved by Corrections staff in a bid to resuscitate him, but this has created tension with the investigating police officers because the potential contamination of evidence.
Spokeswomen for the Auckland City police and the Corrections Department declined to comment about the movement of the body and referred questions to one another.
In a statement, Corrections Department Northern Regional Commissioner Jeanette Burns said death of a prisoner in Corrections custody is a "tragedy" and expressed condolences to his family and friends.
She said inmates are often suffering from extremely poor mental health when they arrive in prison and the care they receive in prison often far exceeds what they were accessing in the community.
"Despite the significant efforts we make, it is incredibly difficult to prevent the actions of someone who is determined to hurt themselves."
Ms Burns said this was a common issue worldwide where mental health disorders and illness is up to five times more prevalent in prisons than in the community.
"In saying this, our staff have saved the lives of approximately 100 prisoners over the last five financial years. These prisoners were involved in self harm incidents where the individual would have been unlikely to survive without staff intervention."