Why wasn't this cop charged for running over a homeless woman?

A cop was making routine rounds by his car on his shift in Cincinnati, which included taking his cruiser in a park and he ended up driving over a homeless lady sleeping underneath a blanket. I'm sure he felt the jolt running over someone! First off, why is a public officer allowed to drive a car in a park where people congregate? And after a thorough investigation by the State Highway Patrol and the local Prosecutors office they determined it was a 'accident' and no charges were filed against him. Also this officer tested positive for Cocaine in his system. This person was on the force for 18 years. If this would have been someone else that person would be facing some charges including wreck less homicide and Failure to Yield, all felonies. Is this just another example of cops protecting there own?