The mother of the prison officer killed at the weekend wants to see security camera footage of the incident at Spring Hill prison, saying the safety of prisoners is being put ahead of the safety of guards.
Jason Palmer was punched in the head while helping two other guards unlock an inmate's cell at the prison on Saturday. He died in hospital on Sunday. A post-mortem has revealed death was caused by complications from blunt trauma to the head.
A prison inmate, 21, appeared in Hamilton District Court on Monday charged with assault.
Detective Inspector Lance Burdett said on Tuesday that it was too early to determine what, if any, additional charges might follow.
Mr Palmer, 33, was the first prison officer to be killed on duty in New Zealand.
His mother, Ada Palmer, is planning to travel from the United States for her son's funeral and will then take his body back to the US.
She said she would like to see security camera footage of the incident to understand more about what happened to her son.
Mrs Palmer said she is being flown to New Zealand by a union representing prison officers. She said Mr Palmer's widow wants to return his body to the United States.