I think this could have been Casey's first idea, but her native laziness quickly kicked in and realized it was too much effort to bury. Tossing out like garbage was much easier. The shovel might have been used to 'sled' the wrapped-up body from the backyard to the trunk of the car. It was getting stinky and messy at that point. "I need more bags, and that laundry bag with handles would be nice to hoist it into the trunk!" Always looking for the easiest way... didn't even look much past the end of her childhood block.