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A riot between gang members at Paremoremo prison in which four inmates were stabbed was a result of escalating rivalry between two notorious gangs.
Police are not revealing what gangs were involved in the dispute but sources have told the Herald it was a dispute between members of the Killer Beez and Mongrel Mob.
Inspector Gary Davey said police would decide next week if charges would be laid.
Officers completed a scene examination in the east division of the prison, which remained locked down yesterday following the attack on Wednesday afternoon.
Officers seized "a number of weapons" which are believed to be homemade knives.
Mr Davey would not say how many weapons were found. He would also not confirm the weapon type, saying those details formed part of the police investigation.
One inmate suffered a moderate stab wound and was held in hospital overnight, he said. Two others were also taken to hospital but were released after being treated on Wednesday. A fourth inmate was treated by the prison's medical staff.
Mr Davey would not say what gangs were thought to be involved.
"Police aren't commenting on anything other than that we're investigating," he said.
"We'll be reviewing video tapes to assess the evidence and also speaking to witnesses. We'll be assessing the evidence early next week to see whether charges will be laid."
The Department of Corrections issued a statement saying it quickly implemented measures to prevent similar incidents in the future.
Northern regional manager Warren Cummins said the maximum number of prisoners allowed out of their cells in the area involved in the incident had been reduced from 12 to six to ensure staff safety.
"Where incidents do occur a full review of processes, procedures and individual actions takes place and where necessary recommendations for change are made," he said.
"Staff are required as part of their duties to conduct a number of cell searches per week in every unit, and in any given week every cell is searched."
Management of the prison had met with the Corrections Association of New Zealand, which represents prison officers, to discuss staff safety.
Despite an increasing prisoner population, serious prisoner-on-prisoner assaults had reduced in the past 10 years, Mr Cummins said.
Corrections Association president Beven Hanlon renewed earlier calls for prison officers to have more protective gear such as stab-resistant vests or Taser stun guns.
He said that since a Paremoremo prison officer was stabbed by a prisoner with a makeshift knife three weeks ago, staff had confiscated 18 of the weapons.
Mr Hanlon said the association requested then to conduct a "lock down" where cells could be searched for illicit items, but that was denied.
In the latest incident, four prisoners had been stabbed and a lock-down was conducted, which sent a message to staff that prisoner safety was more important, he said.
Prisoners made the knives from "anything they could get their hands on", including the prison's window frames, or sometimes by smashing plastic from their television sets, he said.
A review on prison officer security ordered in 2005 by the State Services Commission had still not taken place and Mr Hanlon called for more action on the issue.
