A coroner has found a string of errors in the way prison staff dealt with high-profile inmate Antonie Dixon before his death.
Dixon was found dead in his cell at Auckland Prison at Paremoremo in February 2009, where he was waiting to be sentenced.
He was found guilty at a retrial the previous year of the murder of James Te Aute and severing the hands of two women with a samurai sword in 2003.
In a ruling issued on Monday, Coroner Garry Evans found that Dixon took his own life, which could have been avoided had authorities transferred him to a mental health unit.
Mr Evans said there were many lessons to be learnt from this "sad case".
He said it was seven minutes before Dixon's cell was unlocked by prison officers to give him medical treatment, by which time he was dead.
The coroner said it was unacceptable that an experienced officer was unaware of rules about unlocking prison cells at night and could have opened it sooner. He said a waist restraint used on Dixon was unlawful and had an effect on his mental state.
However, a Department of Corrections spokesperson said on Monday the officer was right to wait and changes have been made.
Jeanette Burns said since Dixon's death, the department has implemented a tactical response team which can open a cell within two to three minutes of an alert being raised.
Ms Burns said as a general rule, there must be four prison officers present to unlock a cell.
The lawyer who represented Antonie Dixon described the report as limp and doesn't provide answers. Barry Hart, who has been struck off as a lawyer and is awaiting an appeal against the decision, said mostly the report is disappointing.
The Howard League for Penal Reform said someone should be held accountable for Dixon's death. Spokesperson Madeleine Rose said Corrections has acknowledged it should have moved Dixon, but hindsight is too late.