After being tasered, pepper sprayed and heavily restrained, Alo Ngata was left face-down in a police cell with an incorrectly-fitted spit hood covering his face.
Although police policy required him to be constantly monitored, it was not until CCTV footage showed his hands not moving and starting to change colour that officers came to his aid.
He died in hospital two days later.
The Independent Police Conduct Authority (IPCA) today released its report identifying multiple failures by the officers who restrained Ngata, who was on meth when arrested for assaulting an elderly man in Auckland's Freeman's Bay in 2018.
Ngata's arrest was difficult and highly physical, and the IPCA found the use of tasers and pepper spray justified.
However, once in the custody unit, officers failed to assess his well-being and interpreted his incoherent attempts to talk as a sign of breathing.
IPCA chairperson Judge Colin Doherty concluded it more likely that this was actually a sign of reduced consciousness.
"They didn't monitor him as they should have, they did not recognise his situation and when it was recognised there was still an unacceptable delay before they came into his cell to assist him."
After spitting blood at officers, the then 29-year-old was fitted with a spit hood, which has a mesh section at the top, the lower section made of plasticised paper to prevent leaks.
CCTV footage showed the plastic part was covering Ngata's entire face, with only the top of his head visible through the mesh section.
A pathologist's report found that the hood could have obstructed his breathing.
It also meant the officers could not gauge Ngata's wellbeing by seeing his eyes or face.
"They wrongly assumed or wrongly interpreted his lack of cooperation as resistance, when we found that that was more likely due to reduced consciousness," Doherty said.
Officers present told the IPCA that Ngata had been struggling as he was carried from the police van to the cell.
The IPCA said CCTV footage showed him apparently unresponsive in the officers' arms, his head bent over his torso before it slumps to one side.
Before leaving the cell they removed his leg ties and handcuffs but kept the spit hood on, which the authority said was unacceptable.
The IPCA has previously recommended better training for custody officers, but Judge Doherty said this was yet to be fully rolled out.
"We understand from police that that's now in train. It was our view that if it had been in train earlier then police would have been greatly assisted in this case by that training."
Auckland City commander Superintendent Karyn Malthus said the circumstances were extraordinary and the death tragic.
"Police acknowledge the IPCA's concern about the role of the custody in this situation and accept that the supervisor should have focused attention on elements such as the spit hood and constant monitoring, however upon realising that Mr Ngata was in medical distress police acted appropriately."
Police launched their own investigation into the incident, which determined that legal causation for Ngata's death was not established and on that basis no one was criminally culpable.
"Police emphasise the fact the pathologist was unable to determine whether the use of a spit-hood in this case had any causal effect on Mr Ngata's death," Malthus said.
"The report also noted the pathologist's finding that removing the spit hood might not have changed the outcome."
She said the conduct of the employees involved in the incident was assessed and it was considered that there was no behaviour that required an employment investigation.
"I acknowledge that the death of Mr Ngata was a tragic event. I would also like to acknowledge the extreme danger to all staff involved in this incident."
Lawyer Marie Dyhrberg, who was acting for Ngata's family, said the report made for disturbing reading.
"I have also read the response of the police and I do have concerns about that response. It would appear that there is a failure to acknowledge the degree and the depth of the police failings during the course of Alo being in police custody," she said.
Ngata's death will also be the subject of a Coroner's inquest.