Police have been found by the Independent Police Conduct Authority to have unlawfully arrested three out of four young people following an early morning incident in the early hours of February 26 last year.
The authority found that the police officer did not know what he was arresting them for, and was simply carrying out instructions given by another officer.
Police had responded that morning to a report that a few people had smashed a window and gained entry into the McDonald's restaurant in Ormiston, East Auckland.
Four young suspects, who were thought to have been involved in the burglary attempt and fled on a stolen vehicle, were later detained in Manurewa by four police officers.
One police officer put a suspect into a headlock and took him to the ground and twisted his finger in the course of the attempt to restrain him.
The suspect lodged a complaint to police about the headlock and said an officer had twisted his finger.
Although the authority found the injury was probably caused by the two arresting officers, it was likely to have been accidental. It also found the force used to restrain the suspect was reasonable in the circumstances.
However, the authority was concerned that the arresting officer was not sure of the reason why he had arrested the young people for.
"It was also clear that the arresting officer had not turned his mind to the requirements of the Oranga Tamariki Act 1989, which applied to three of the four people arrested as they were under the age of 17," the authority said in a statement.
It found that three of the four arrests would have been lawful had the arresting officer turned his mind to the reason for the arrests and the law as it relates to young people.
Authority chairman Judge Colin Doherty said: "More proactive communication between [the arresting officer and his supervising sergeant] would have prevented the confusion."