Corrections chief Jeremy Lightfoot says the Waikeria Prison riot was "spontaneous" and "not born out of complaints", contradicting families who said objections to prison conditions were ignored.
Lightfoot also revealed that eight men escaped from their cells at the prison through high windows, with the help of a group of inmates who escaped early on by lighting several small fires in the yard and gaining access to the roof.
Lightfoot spoke to the Justice Select Committee on Thursday about how the prison riot unfolded, revealing he was advised on the afternoon of December 29 that several prisoners in a yard at Waikeria Prison had started to light a number of small fires.
Later that night, around 200 men were evacuated out of the top jail facility - which is now destroyed - while fires continued to burn, "threatening their safety and obviously the safety of our staff".
Lightfoot said he wanted to be "be clear" that while the men described their behaviour as a protest, their actions were "violent and put hundreds of people at risk", throwing doubt on the inmates' claims that they were protesting against their treatment in prison.
"It exposed them, other prisoners, our staff and emergency services to significant danger and caused a huge amount of trauma for those prisoners that were evacuated from the top jail and difficulties for those who were on site," Lightfoot said.
"There is no excuse for what they have done."
Family members of the rioters said in January their complaints about conditions at the prison were dismissed before the incident took place.
In a statement issued through People Against Prisons Aotearoa, whānau members said they tried "many times" to make complaints to the prison and the Department of Corrections and were "dismissed every time".
They claimed the jail was "unfit for humans to live in", and that the jail was "unhygienic and conditions inside were disgusting" and that Corrections forced them to endure it.
Lightfoot disputes the claims.
"Having been directly involved throughout those six days, I would say they weren't particularly clear," he said of the prisoners' demands.
"Throughout the six days they changed, and it was clear to me that the activity was spontaneous and was something that was generated out of in-the-moment frustration, rather than anything that we had a heads up or intelligence around.
"We aren't clear still what the real motives were around it, but it is clear that the things that they were purporting to be protesting around were not born out through any complaints that had been lodged prior to the incident having occurred, and all of the many channels of opportunity that those men had to lodge any of those complaints."
A 25-year-old man was the first to be charged in relation to the incident and was accused of rioting, using weapons, and unlawful damage. He was one of 17 men accused of instigating the fiery uprising.
The prisoners surrendered on January 3, and received food, water and access to medical staff after it was withheld as that could form part of the negotiating process.
Lightfoot said how the riot unfolded "speaks to the spontaneity" of it.
"Fires were lit in the yard that enabled a limited number of those men who were in the yard to gain access progressively to a roof area. The make-up of this very old facility - first constructed in 1911 - are relatively closely linked together, so once you're on the roofs you can gain access to other parts of the site," he explained.
"The way in which those eight men were extracted from their cells was I believe through windows at the high level, but that did require quite some effort. But I would also acknowledge that the infrastructure is not a modern prison build which is why we had plans to rebuild with new assets in the lower jail."
He said the barred windows were able to be attacked from both the inside and outside. From the roof there were "sustained assaults" and those on the roof were able to fashion tools.
National MP Simeon Brown said it was "refreshing" that Lightfoot described it as a "riot" and not a "prisoner disorder event" like Corrections Minister Kelvin Davis did.
"The formal adoption from our records of calling it a riot is just something that we haven't fully worked through administratively, but there is no question that the events that occurred over those six days were a riot," Lightfoot said.
Davis said his top concern through the Waikeria event was for the safety and wellbeing of staff, which is why he made the decision "not to bow to the demands of the prisoners" nor make a public comment until after it was over.
"I said at the time, that the actions those prisoners took, and the significant risk they put themselves and others in, were completely unacceptable and in no way justifiable. I, like many others, await the outcome of the many reviews underway, including the police investigation."
A new high-security prison with a modern mental health facility - split between 500 prison beds and 500 mental health beds - is currently being built at Waikeria Prison and will open in 2022.
The overall prison population has reduced from its peak of 10,820 in March 2018 to today's number of 8682, which Lightfoot said has meant Correction could absorb the impact of losing part of Waikeria Prison.