Four NSW police officers who accused an Aboriginal man of assault, beat him while he was in custody and then lied about their actions, will have their evidence tested by the Police Integrity Commission (PIC).

A public hearing by the PIC begins in Sydney on Monday into the arrest and prosecution of Corey Matthew Barker, 22, at Ballina on the NSW north coast.

Mr Barker allegedly threw a plastic bottle toward police who were apprehending others on the evening of January 14, 2011. He also was charged with resisting arrest and assaulting police.

During the court process, the charges against him were dropped and in July 2012 the prosecution was ordered to pay his legal costs of $30,000.

Ballina Local Court Magistrate David Heilpern also referred the matter to the PIC after CCTV footage from inside the police station challenged the officers' testimony.

The officers had told the court that Mr Barker punched Senior Constable David Hill in the nose while he was being transferred from the police dock to a cell.

The constable said he then "jammed" Mr Barker against a wall before the other officers helped restrain him on the ground.

He gave his evidence under the belief the footage of the incident had been damaged.

"The video becoming unplayable is suspicious," Mr Heilpern said in his costs judgment.

"It beggars belief that the video just happened to be unavailable for that incident."

The tapes were later repaired and the video showed that Mr Barker did not break free of the officers nor did he punch anyone, the magistrate said.

"I have concluded that Senior Constable Hill was lying."

The footage also showed Senior Constable Ryan Eckersley kicked Mr Barker in the head while the officers were on top of him.

"Even Senior Constable Eckersley stated that it looks like that," Mr Heilpern said.

When Constable Lee Walmsley was shown the video, he changed his previous evidence and said the punch must have happened before the events in question and that there was more than one punch.

On another issue, Mr Heilpern deduced that Constable Walmsley lied about speaking to Senior Constable Hill who told him that the video footage of the incident had been resurrected.

"I am satisfied on balance that the officer has lied on oath about this issue in an effort to mislead the court and attempt to ensure it was not aware of witness collusion," he said.

Senior Constable Luke Mewing told an identical story about the scuffle but when later shown the video he became unsure and confused about the incident.

He did agree that three officers were already on top of Mr Barker when he delivered a knee-strike to his side as "pain compliance".

Mr Barker arrived at the police station with no injuries but left with significant injuries to his face.

"It is indeed fortunate that the video could be recovered," Mr Heilpern said.

"Without it, this grave injustice would in all likelihood have never come to light."