Police acknowledge decisions made during an operation in which a man was shot dead by an officer weren't well thought through.
Officers chased Lachan Kelly-Tumarae's car for 18km before he stopped and pointed his gun at them in Omahu, near Hastings, in 2011. An officer then shot at the 19-year-old 14 times.
The Independent Police Conduct Authority released its findings on Thursday, saying officers did not comply with some policies, such as a lack of clarity of who was in charge and what tactics to use during the operation.
It says at times police acted instinctively, instead of complying with a disciplined and cautious approach.
The authority heavily criticised police for parking a patrol car right beside Mr Kelly-Tumarae's car, because they were unable to safely contain him and put their own lives at risk.
However, the authority's report says the officer who fired 14 shots at Mr Kelly-Tumarae and killed him was justified because he believed his life was under threat.
It says police could have done a better job when communicating with Mr Kelly-Tumarae's family, noting they failed to explain the number of gunshot holes found in his clothing when his body was returned to his whanau (family).
Assistant Commissioner Mike Rusbatch says police accept the authority's findings.
"In hindsight, I know the police officers know that their judgement stopping next to the vehicle was probably not well thought through. But the threat that had been proposed on our police officers was a continuing one."
Police say they are working on the report's recommendations relating to improvements to aspects of their firearms policy.
Radio New Zealand has been unable to contact Lachan Kelly-Tumarae's family.