MISSISSAUGA, Ont. - Ontario's police watchdog is looking for a driver who may have witnessed a fatal collision between a cyclist and an unmarked police vehicle.

The Special Investigations Unit says 85-year-old David Nesbitt was struck by the unmarked provincial police SUV on March 13 in Orillia and died in hospital a few days later.

The SIU says the collision occurred around 4:45 p.m. as Nesbitt rode his bike on Atherley Road near Gill Street, by a Giant Tiger outlet.

Investigators say a husband, wife and child in a silver-coloured vehicle were believed to be following the black SUV and the driver may have seen the collision.

They are asking the man -- and anyone else with information -- to contact investigators.

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