A police officer in Victoria's Latrobe Valley, east of Melbourne, has been convicted of punching a prisoner in the head multiple times in an attack that was caught on camera.

Key points: Senior Constable Dallas Howell was found guilty of assault in March, 2019 but appealed against the conviction

Senior Constable Dallas Howell was found guilty of assault in March, 2019 but appealed against the conviction Security footage from inside the cell shows Howell assaulting prisoner Daniel Hornsby

Security footage from inside the cell shows Howell assaulting prisoner Daniel Hornsby Howell's lawyer said the conviction meant it was unlikely Howell would be able to return to the police force

Senior Constable Dallas Howell was found guilty today in the County Court in Morwell of two counts of unlawfully assaulting Daniel Hornsby in the Moe police station cells on September 8, 2017.

Howell was convicted of the same offences in the Latrobe Valley Magistrates Court in March last year but appealed against the decision.

During an appeal process, the original decision is set aside and the matter is heard again in the County Court.

Security footage from inside the cell shows Howell approach Mr Hornsby and drag him to the ground after the prisoner kicks at him. Howell is also seen punching the prisoner in the head multiple times in two separate incidents.

Howell said he was acting in self-defence.

But Judge Carolene Gwynn said the evidence against Howell was "overwhelming", and recorded a conviction and placed him on a 12-month good-behaviour bond.

"It is serious offending and, in my view, a clear message needs to be sent," Judge Gwynn said.

She said it was important to send a message that police were not "a law unto themselves".

"I'm not satisfied that the appellant believed it was necessary to do what he did to defend himself," she said.

"Rather, it was Mr Hornsby who appeared to perceive the need for self-defence."

Police witnessed the assault

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 1 minute 10 seconds 1 m 10 s Police officer convicted of assault ( Supplied: County Court of Victoria )

Three police officers present at the Moe Police Station that night testified that they saw Howell punch Mr Hornsby in the cells.

The court heard Mr Hornsby was arrested and taken to the station after having an argument with his then girlfriend.

He told the court that prior to his arrest, he had consumed alcohol, cannabis, ice and Valium.

Senior Sergeant Melissa Blair was the sergeant in charge of the station when the assault occurred.

She told the court Mr Hornsby had been verbally abusive and she had decided to do a welfare check with Howell on the prisoner.

Senior Sergeant Blair told the court Howell entered the cell and the fight broke out after Mr Hornsby "lightly" kicked at Howell's leg.

She told the court Howell later apologised and told her he had "snapped".

Potentially career ending

Howell's lawyer, Nadia Kaddeche, told the court her client had paid a high price over the assault.

Ms Kaddeche said the conviction meant it was unlikely Howell would be able to return to the police force.

The court heard he had been a police officer for about eight years and had served as an acting sergeant and had served eight years in the military, which included service in Iraq and Kuwait.

He also received character references from local police and the local MP, independent Russell Northe.

Judge Gwynn said she accepted Howell was of good character but the sentence needed to provide a deterrent.