The youth, who was a passenger in the car, gave the officer a false name. He was not legally required to give his name but the officer insisted.
The police officer checked the database and found the youth's true identity, which also showed he was breaching a condition of bail set by the court that he observe a curfew.
The fact he was 17 years old was also in the database, which legally meant that he could only be arrested if he has breached Youth Court bail on two or more previous occasions. This was the youth's first breach.
The officer also entered a house to search for the young man which the Authority said was unlawful because he did not have the occupier's informed consent to enter.
The young man fled and the officer tracked him with his police dog, catching up and releasing the dog on him as he entered some bushes. The dog bit the 17-year-old on both arms.
A witness who overheard the arrest and complained to the Authority said the officer used "excessive force on the youth".
Authority chair Judge Colin Doherty said the young man's arrest was unlawful because the policeman did not have reasonable cause to treat him as an adult and arrest him for his first breach of bail, and the use of a police dog was also unlawful.
"The officer does not have a legal defence of using force 'in good faith' to carry out an unlawful arrest," he said.
Even if the officer had legal cause, he was not justified in commanding the dog to bite the young man.
It was not reasonable or proportionate to the seriousness of the youth's breach of curfew, the need to detain him to bring him to justice, or the degree and severity of risk he posed if he escaped.
The Authority also found that the officer spoke to the youth and the witness in an unprofessional manner.
Police acknowledged but disagreed with the Authority's findings, saying its internal review found the officer's use of force was "justified and proportionate".
Wellington District Commander Superintendent Corrie Parnell said the officer had reasonable grounds to believe the arrest was necessary "not only for the breach of bail, but because the youth was involved with a gang, was on bail for serious charges... and was running from police."
Using the police dog was also necessary to prevent the young man from escaping, Parnell said, but agreed the officer's language was unprofessional.
"The officer's language and attitude during this incident fell well short of NZ Police values and what we expect of our people," he said.
"This has been addressed by way of an employment investigation and sanction."
