The man was in court cells in January 2023, challenging staff to fight, and threatening the officer.
"I want to shoot you and your family," the man said.
The Independent Police Conduct Authority said after this, the man went on swearing at detainees in other cells.
He refused to return to his cell when instructed, instead repeating his challenge and threatening the officer once more, as he moved closer.
CCTV footage shows the officer punched the man in the side of the face, knocking him into the wall as he tried to step past.
The Independent Police Conduct Authority said the officer had less forceful options he could have chosen, though the officer said he acted in self-defence, believing the detainee was going to assault him.
"He could have moved away from the man or pushed him away to redirect him," the IPCA said.
The IPCA accepted that police did not have enough evidence to charge the officer with assault, but noted that the officers no longer works for police.
Police Acknowledge Findings
Counties Manukau relieving district commander, Inspector Alison Brand, said while police made enquiries into the incident, there was not enough evidence to charge the o.
"[On] 24 January 2023 police received a complaint from someone being held in the court cells that they had been struck on the side of the head by an authorised officer," she said.
Police said they launched an employment investigation into the matter and could advise that the employee was no longer working for them.
RNZ
