Ontario's police watchdog is looking for two witnesses to an arrest during the G20 that left a man with a facial fracture.

The Special Investigations Unit says it has images of two men holding what appear to be cameras pointed at a group of officers making the arrest.

The images come from a video at the centre of the unit's probe into injuries sustained on June 26 by Adam Nobody.

The unit says it wants to talk with both of the men as part of their investigation.

Nobody, 27, was at a demonstration at the Ontario legislature and started to run away as police ordered people to move back.

As he ran Nobody was knocked to the ground by an officer in riot gear and arrested, the SIU has said.

He was treated in hospital for a fracture below his right eye.

The SIU concluded last month that there appeared to be an excessive use of force, but it was impossible to tell the identity of the officer from the video.

The unit closed the case, saying there were no grounds to lay charges, but it was reopened last week — one day after Toronto police Chief Bill Blair ripped into the SIU.

Blair alleged the video of the Nobody arrest that the SIU said corroborated an excessive use of force allegation against police had been "tampered with" since about five seconds of audio and video were missing.

The SIU countered, saying it received a sworn statement from the man who shot the video that it had not been edited, and that the gap occurred when he stopped his camera because he thought he might have to retreat from advancing police.

Blair then issued an apology, saying he didn't mean to imply the gap was deliberately done or that there was any intention to mislead.

More than 1,000 people were arrested during the summit. Of that group about 300 were charged and five months later, few are still facing those charges.

The Special Investigations Unit is asking the two potential witnesses to contact them at 416-622-1806 or 1-800-787-8529 ext. 1806.

YouTube video of Nobody's arrest.