The Independent Police Conduct Authority has ruled the force used by four police officers against a man in a holding cell was unnecessary, unreasonable and unjustified.
Rawiri Falwasser was arrested in Edgecumbe in 2006 and repeatedly sprayed with pepper spray on the arms and face, and hit with batons on his forearm and head.
Five cans of pepper spray were used and Mr Falwasser received a 6cm cut to his head.
Sergeants Keith Parsons and Erle Busby, Constable John Mills and Senior Constable Bruce Laing were trying to move Mr Falwasser to a separate observation cell.
The Whakatane officers were acquitted of any criminal wrongdoing in a trial in 2008, after which internal disciplinary proceedings were launched.
In its report, the IPCA says Mr Falwasser showed no aggression until he was sprayed, there was no urgent need to move him and pepper spray exacerbated the situation.
However, the authority has not made any recommendations.
The union for police staff says the officers were not acting in a malicious or brutal way.
Police Association president Greg O'Connor says the men acted the best they could.
"What we had was four officers dealing with a situation that confronted them the best way they knew how. These were four experienced officers; they had to do what they believed what was necessary to resolve that situation.
"They may have done it differently another time, however, it was never criminal."
Two of the officers are no longer in the police and Rawiri Falwasser's mother says the remaining two should not be either.
Kihi Falwasser says being honest is important for police officers, and the men are not role models.
Mr Falwasser was awarded $30,000 by the High Court earlier this year.