Five inmates have been charged over an attack which left a Rimutaka Prison guard in an induced coma with serious head injuries.
The prison officer remains off duty following the attack on 1 June when he intervened to help an inmate who had been set upon by a group of prisoners.
A total of 22 charges have been laid against five prisoners aged between 18 and 28.
The police are not naming the men but say all are charged with injuring with intent to cause grievous bodily harm, among other charges.
The 28-year-old faces 11 charges including two counts of assault with a weapon.
All five are due to appear in court next week.
The Corrections Department has described the attack as savage, and praised the injured officer for his courage.