Police were justified in setting a dog on a man who had previously attacked officers with a blood-filled syringe, a report says.
The Independent Police Conduct Authority (IPCA) found the dog handler believed the man posed a risk of serious injury to his fellow officers.
The man has a history of violent offending, including using a blood-filled syringe to assault police.
On August 24 last year police found out the man intended to pick up a prescription in Upper Hutt. He was wanted at the time for serious assault.
Police set up cordons and approached the man as he came out of the pharmacy, telling him he was under arrest.
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The man fled into an underground carpark, where he was cornered by police. During the ensuing struggle, the man fell to the ground with two officers holding his arms as they tried to place him in handcuffs.
A dog handler who knew of the man's previous criminal history arrived on the scene.
He saw the man's hands were underneath him and was concerned the man would possibly use a weapon, such as a blood-infected needle, on the two officers.
The handler instructed his dog to bite the man on the foot, and the officers handcuffed the man.
Police then took the man to hospital to receive treatment for his seriously injured foot.
"The dog handler's assessment of the circumstances led him to believe that the man was assaultive and posed a genuine threat of retrieving and using a weapon such as a knife or needle," said IPCA chairman Judge Colin Doherty.
"In that case the use of his dog was an appropriate option, as significant force was required to immediately overpower the man and eliminate the risk of serious injury to the officers who were struggling with him in the course of arresting him."
However, the IPCA found the dog handler failed to give the man the required warning before using the dog.
It also found the first two officers used reasonable force when physically restraining the man, and that police provided appropriate medical assistance.
Hutt Valley Area Commander Inspector Sean Hansen said police dealt with "fast-moving and ever-changing situations every day".
"Split-second decisions need to be made to keep the community and police safe.
"Every day our staff are committed to keeping the community safe and that was the priority for our staff during this incident."