Corrections top brass has been grilled over the Waikeria Prison riots which led to a six-day standoff between staff and inmates.
And National is calling for an independent probe into the impact of the rising number of gang-affiliated inmates after Corrections confirmed every single rioter was gang-affiliated.
Head of Corrections Jeremy Lightfoot said the six-day stand-off started on the afternoon of December 29 when some of the 21 men in the prison's yard lit fires.
The rioters then made their way to the roof of the 100-year-old "top jail" and fashioned tools to get others out of their cells through the windows.
"I want to be clear. While the men described their actions as a protest their actions were violent and put the lives of hundreds of people at risk.
"It exposed them, other prisoners, our staff and emergency services to significant danger and caused a huge amount of trauma to the prisoners who had to be evacuated from the top jail and difficulties for those remaining on site. There is no excuse for what they have done."
About 200 men had to be evacuated from the top jail as the fires threatened their safety.
Lightfoot said the demands of the rioters were unclear, changed over the six days and spoke to the spontaneity of the protest.
"We aren't clear what the real motives were around it. But it is clear that the things that they were purporting to be protesting around were not borne out of any complaints that had been lodged prior to the incident having occurred."
Every single one of the rioters was gang-associated, Lightfoot said.
Corrections Minister Kelvin Davis has previously said the "majority" of the men involved were members of the Mongols and Comancheros gangs, including five 501s or deportees from Australia.
Two investigations are underway - one is an operational review by the Chief Custodial Officer.
The other is being conducted by the Chief Inspector of Corrections and will investigate and report on the circumstances surrounding the riot and the department's response.
But neither will not specifically assess what impact a rising population of gang-affiliated criminals has had on the prison system.
National's Corrections spokesman Simeon Brown said his party wants an entirely independent inquiry into the riot which will look at what role organised crime and gangs played in it.
"This was a violent riot that destroyed millions of dollars of prison infrastructure and put the lives of Corrections staff and prisoners at risk.
"The narrow terms of reference suggests Corrections isn't interested in learning anything new and making sure this doesn't happen again."
But Lightfoot said the terms of reference for the inquiry were intentionally left wide in scope to provide the Chief Inspector with the ability to investigate all elements of the circumstances contributing to and surrounding the riot as she sees fit.
"It is my expectation that the impact of the gang affiliation of prisoners involved will be one of many factors considered," he said in a statement to the Herald.
Lightfoot told the select committee that the age of the building aided the rioters which is why there were plans to build a new facility.
Last August, the Ombudsman published a report following an unannounced inspection of Waikeria which found the high-security areas were old and not fit for purpose.
Peter Boshier later described the conditions in the "top jail" - which was destroyed by the riot - as "decrepit" and "bordering on inhumane".
Lightfoot told the select committee Waikeria's infrastructure disrepair was unique among Corrections facilities.
The building was insured for $4.5 million plus GST but the true costs of rebuilding the facility is not yet known.
The riot over the New Year holidays was the biggest in New Zealand for decades.
The destruction of Waikeria's high-security complex required more than 200 inmates to be moved to other prisons.
Seventeen men have been charged over the riot.