That rule is in place in Intervention and Support Units, set up for prisoners with high mental health needs, due to the risk of self-harm.
A police spokeswoman said the investigation continues.
"One person has been charged with other assaults with weapons in relation to the events prior to the incident and will appear in the Auckland District Court on May 17.
"As the matter is before the court, police have no further comment."
The Herald understands the person charged is a corrections officer at Mt Eden prison.
Corrections Acting Regional Commissioner Tayla Yandall said in a statement the staff member involved had been placed on special leave.
"On Wednesday 11 May, Corrections was informed that Police have laid a charge against a staff member in relation to the circumstances prior to the death of a man at Mt Eden Corrections Facility on Tuesday 5 April," the statement said.
Yandall would not comment on the circumstances of the death.
"As the matter is now before the courts, and still subject to reviews and investigations, we are unable to provide specific comment on this case at this time to avoid prejudice to the outcome of the court proceedings and investigations."
The man died shortly after he was allegedly pepper-sprayed and restrained, it is understood.
Prison staff tried to revive him but he died at the scene.
The name of the prisoner who died was suppressed on an interim basis by Coroner Alexander Ho after an application by the inmate's uncle.
A minute from the Coroner, dated April 8, shows he had not yet decided whether to open an inquiry due to the possibility police would lay criminal charges.
"If criminal charges are laid and the matters required to be established by me under the Coroners Act are established instead in the course of that criminal prosecution it may be that a coronial inquiry never becomes necessary," Coroner Ho's minute said.
"I therefore consider it appropriate for the court dealing with any criminal prosecution to determine in the course of that proceeding whether [the victim's] name ought to be permanently suppressed."
The uncle also applied for suppression of the circumstances of the man's death on the basis it would breach the family's privacy, and that younger family members would struggle to hear about the mental health issues he faced in prison.
This part of the application was declined by Coroner Ho.
"The family can have no legitimate privacy concern or concern for younger family members as a result of the media publishing details of the death, given that [the victim's] name cannot be published in connection with any such reports."
The Crimes Act charge of assault with a weapon carries a maximum term of imprisonment of five years.
