(Radio Iowa) — Des Moines police are looking into a crash yesterday (Sunday) afternoon that killed the driver and left his son injured. Police say the car was driving along Grand Avenue near the governor’s mansion when it went out of control, over a concrete retaining wall and crashed onto a parking lot below. The driver, 32-year-old Grant Stokka of Des Moines, was killed, while his eight-year-old son survived with minor injuries. Investigators say it does NOT appear speed, road conditions or impairment were factors, but they believe another vehicle may’ve caused Stokka to quickly veer. Witnesses are asked to come forward.