The use of a taser on a handcuffed Greymouth man who was resisting arrest has been ruled unjustified by the Independent Police Conduct Authority (IPCA).
The IPCA has ruled that officers breached policy when a sergeant directed a probationary constable to taser the man, and the use of a contact stun - the activation of a taser while it is directly applied to the body - was a "disproportionate and unjustified use of force".
RNZ has learned that the sergeant was Matthew Frost, who has since resigned from the police.
The incident started at about 9pm on 20 June 2015, when police were called to a domestic incident between neighbours in Greymouth.
The IPCA said a man had come to his neighbour's house, drunk and armed with a tomahawk, but when police arrived they were told that the man was no longer armed and had gone back home.
The man had mental health issues, and police decided to delay an arrest until the morning when he would have sobered up.
But police were called back at midnight and officers found the man and a friend sitting in a car.
The man was arrested for the tomahawk incident, but he and his friend refused to get out of the car. Pepper spray was used on the friend and after 20 minutes, officers managed to handcuff the pair and escort them to a police van.
The taser was used twice when the man refused to move his foot from the van cell door.
IPCA chair Judge Sir David Carruthers said a taser could only be used on a person who was assaultive.
The Authority also found that the sergeant should not have directed the probationary constable to use the taser.
"The junior officer was put in the unenviable position of feeling like refusal was not an option, given the sergeant's seniority," said Sir David.
The Authority also determined that the sergeant should have declared that he had instructed the probationary officer to use the taser and that he incorrectly recorded that the use of taser complied with police policy.
In a statement, police said they accepted the findings.
"We agree with the IPCA that the use of taser in this instance was unjustified and the sergeant should not have directed an inexperienced officer to contact stun the man because he was not being assaultive," said Superintendent Steve Kehoe, Tasman District Commander.
"We understand the pressure felt by the probationary constable to follow their supervisor's orders and have provided advice around this matter to them."