This restraint was necessary given the level of aggression and abusiveness Harris had shown towards staff, he found.
But Harris' mother, Te Enga, says the use of force on her son was not justified, given his high-risk condition and delicate health.
"I'm very upset.
"Whatever Nicholas' behaviour was, because I was told he was being aggressive and abusive, these words are really important because that's how they justify what happened to him.
"It's not good enough."
Nicholas' brother Brendon said the seven-minute restraining process during which Harris was held down by at least eight Corrections staff was completely inappropriate given his weight, chronic asthma, diabetes and heart problems.
"Someone of his size, just for him to get off the ground would take a lot of effort. So when he's got nine people on him, that's definitely pushing him to the limits," he said.
"They're supposed to be there to care and protect him but they compromised that," Te Enga added.
The coroner said that it was clear that Harris' attitude and behaviour towards the Corrections officers had been major contributing factors in his death.
This behaviour had "necessitated a robust spontaneous control and restraint process".
In a statement issued shortly after the release of the Coroners' report, the Department of Corrections expressed their concerns about the death.
"As well as a loss to his family and friends Mr Harris's death has been tremendously stressful for our staff who have been very affected by this. No one wanted or intended that this tragic event would occur.
"It is Corrections' belief that it was absolutely necessary to enter his cell as he was harming himself. It was also imperative that staff entering his cell to prevent him harming himself took steps to ensure their own safety. The method used to restrain Mr Harris was standard practice in this type of situation."
Police investigations concluded there was no cause for prosecution and an investigation by the Department determined that its response was measured, it said.
But Te Enga said given his mental state at the time, Nicholas should never have been in the standard cell, but in the Kotuku Unit for high-risk prisoners.
An original order by the judge to send Nicholas to the Kotuku Unit was overturned by Corrections staff, she said.
"He should never had been in the mainstream cells, " she said.
Brendon agreed the decision to remove Nicholas from the high-risk cells was a mistake.
"There were a lot of mistakes made [by management], without those mistakes he wouldn't have been in the position he was in. Fair enough he was restrained but had they done their proper job, he shouldn't have even been in there. He should've been in a mental health ward."
Te Enga said the family was allowed to see the footage but have been denied a copy.
"We're not allowed to have this footage and I think that's disgusting."
They were also not permitted to listen to the audio.
"The audio was really crucial, because there was evidence that he never spoke during [being restrained] at any time," said Brendon.
During the seven minutes that Harris was being restrained, there was no record of him resisting or saying anything to staff, Brendon said.
"It was only after the six or seven minutes of restraining him that they checked to see if he was alright and found that he was unconscious," said Brendon.
"Why would they let him lie silently for minutes before checking he was OK?"
For people with years of experience, to restrain someone who didn't say anything was unusual, he said.
The family wants to see a change in restraining procedures, dependent on health conditions and size.
"They need to work something out so that this will never happen again," said Brendon.
"Obviously in Nick's case - he is not your average sized human being - any person that big, there should be a different way to restrain them."
Putting them on the ground is "not a good option" because the weight alone could asphyxiate them, he said.
"They have to change the procedure - that's the least we want," said Brendon.
"They could do it to someone else and that would be devastating."
In its statement, the Department said it would be carefully reviewing the Coroner's findings and would "respond appropriately".
"If changes are required to training and procedures we will make them."
But the Harris family wants every case to be treated differently, with Corrections officers to consider prisoners' health and size.
"They held him down until he died," said Te Enga.
The Harris family is meeting with their lawyer this week to see what their options are.
"I want to take it to court because I'm disputing them," she said. "We want to take it higher."
