Conventional Parking Brake problems of the 1998 Jeep Grand Cherokee

I parked my Jeep in front of the grocery store and left it running. I got out walked around the front to go into the store when I heard a noise. I turned back to the car, opened the passenger door, the car was rolling backward. It knocked me down, and the right front tire ran over my left foot and leg and the toes of my right foot. The car proceded across the street, entered the parking lot of the court house and hit another parked car.