MISSISSAUGA - Ontario's police watchdog says it's again been unable to identify any officers involved in a G20 arrest that a man claims left him with serious injuries.

The Special Investigations Unit had reopened the case of Dorian Barton who claimed his arm was broken when he was assaulted by police during last June's G20 demonstrations in Toronto.

Civilian witnesses told the SIU that Barton, who was taking pictures of mounted police officers, was struck with a riot shield and then hit with a baton after he fell to the ground.

The SIU says none of the civilian witnesses was able to positively identify any of the officers involved.

Photographs of the incident were shown to 11 officers, but the SIU says none of the officers could identify the perpetrator.

Director Ian Scott says without a positive identification, the SIU has concluded that there are no reasonable grounds for charges to be laid against any Toronto police officers in Barton's arrest.