TORONTO -- The province's police watchdog has opened an investigation into an arrest they say left a Toronto man injured with permanent scarring to his forehead.

The Special Investigations Unit says they only recently learned in media reports about the case of 30-year-old Raymond Costain, who was arrested in the city's downtown back in April 2010.

The agency says Costain was struck several times during his arrest, and that medical records show he was left with a permanent scar mark.

The SIU says a judge at Costain's trial ruled police used force that was "unnecessary, unjustified and excessive."

The SIU is an arm's length agency that investigates reports involving police where there has been death, serious injury or allegations of sexual assault.