MISSISSAUGA, Ont. - The Special Investigations Unit says a Toronto police officer was justified in fatally shooting a man who was wielding a knife on a city bus.

Police were called Aug. 29, after Reyal Jensen Jardine-Douglas, 25, of Pickering, Ont., got on a bus and was reported to be acting irrationally.

The SIU says police stopped the bus and after an officer boarded the vehicle, Jardine-Douglas reached into a bag and produced a knife.

Jardine-Douglas refused numerous commands to drop the knife and followed the officer as he backed off the bus.

The officer fired four times -- hitting Jardine-Douglas twice -- after the man got off the bus, but refused to drop the knife.

SIU director Ian Scott says the officer backed off the bus, issued numerous commands to drop the knife, and continued to retreat until he was backed up against a hedge.

"In my view, the subject officer was justified in using lethal force," Scott said Thursday in a release.

"I am of the opinion that the subject officer had a reasonable apprehension of imminent grievous bodily harm or death," Scott said.