According to a news release from the SIU, there was an interaction between York Regional Police officers and a 22-year-old man in Aurora at 9 p.m. Saturday.
Officers "discharged their firearms," and the man was then taken to a hospital in Toronto where he was pronounced dead.
Seven investigators are now involved with the SIU probe. Any witnesses are asked to contact the lead investigator at 416-622-1898, or 1-800-787-8529, ext. 1898.
Tweets from the York Regional Police account indicate that officers had been responding to a report of "a man with a gun" in Aurora on Saturday night.
The SIU investigates all incidents involving police in which serious injury or death occurs, or when allegations of sexual assault are raised.