The police watchdog has found an officer unjustifiably kicked a man and aimed a pistol at his head following a pursuit in Taupō.
Three men with crowbars fled police after robbing a supermarket in the town in April 2018.
Officers spiked the tyres of the car they were driving and attempted to keep it in its lane, because the driver lost control, to protect other road users.
The Independent Police Conduct Authority (IPCA) has ruled the pursuit, and the measures officers took to force the car off the road, were justified.
After the car stopped, the first officer on the scene presented his firearm at the driver and pulled him from the car.
A witness reported the officer then lunged at the man "as if to punch him" while he was handcuffed. The IPCA said there was no justifiable reason for doing this.
Witnesses also said the officer held a pistol to a passenger's head and kicked him as he lay handcuffed on the ground.
The officer denied kicking the passenger, but the Authority said it was satisfied it did happen and was unjustified and unreasonable.
"The officer said he initially thought the man was secured but had not confirmed this himself. When the man swore at him and rolled over slightly, he thought he posed a threat, so dived on top of him with his pistol still in his hand.
"His pistol was pointing towards the man's head and may have accidentally touched it. However, witnesses gave different accounts of the incident."
IPCA Chair Judge Colin Doherty said the passenger was not in a position to escape custody and did not show any intention to.
"Although the officer has argued that he believed the passenger did pose a threat of resistance and escape, the Authority does not accept he actually believed this. Furthermore, even if that belief was genuine, it was not reasonable."
The officer faced two assault charges, but was later acquitted following a jury trial earlier this year.
Police have acknowledged the findings and said a fellow officer raised concerns about the officer's actions, as well as witnesses.
They were then stood down from duty and remain stood down, as an employment process in relation to this incident is ongoing.