Although the New South Wales police officer was charged more than a year ago, he remained in his post at Goulburn Police Station on “restricted duties”.
The CCTV footage, which presents the assault from several angles, shows Senior Constable Jeames Iain Murray grabbing Patrick Little, who was 18 at the time, by the neck. He gets him into a headlock and hurls him at a wall and later at a custody cell door.
Murray was found guilty of two counts of common assault, and was fined $3,500 (£1,895). He had a conviction recorded, with the magistrate finding the severity of the assaults and his abuse of the position of trust warranted it.
"He was the adult and unfortunately he reacted in a way that was not appropriate, as I've found," she said.
Magistrate Susan McGowan said “there’s no circumstance where this was warranted”, adding that while she “recognises the difficulties of modern-day policing" it has to "step up".
The charges against the serving senior constable followed a complaint which led to an internal investigation into the incident.
The assault took place on 12 January, after Mr Little was arrested for fighting outside a club. He resisted initially but then cooperated and was put in the back of the police van and taken to the station.
Footage then shows the assault, which Murray – who pleaded not guilty – admitted did not look good. However, he claimed the videos, which show the scene from multiple angles, did not tell the whole story.
The magistrate found Murray’s claims that his actions were lawful and proportionate “inconsistent” with what was shown in the bodycam and CCTV footage.
A New South Wales Police spokesperson said: "The officer remains on restricted duties; his employment status is currently under review."