At the police station the officer hit the man with an uppercut to the face, which was captured on CCTV.
A police employee said the officer then threatened to kill the man.
The officer denied threatening or punching the man, despite the footage. He was charged and pleaded guilty in court to two counts of common assaultand one of threatening to kill. Two other charges were withdrawn.
The officer was discharged without conviction in January this year.
An employment investigation followed bu the officer resigned before it was finished.Auckland City District Commander Superintendent Karyn Malthusagreed that the officer used excessive force after the arrest.
"He acted out of line and abused his position of authority. It is never okay for our officers to act, or react, in a violent manner."