I wonder if the police have Allison's car keys. Wherever her car keys are, are probably where this all went down. Somehow, the keys were lost, thus them not being able to start the car to bring it home. Car was towed in neutral, reason it looked so close, only had parkers on, to keep safe and maybe lights so close, would annoy front driver anyway.
Or as they were dumping body....keys fell out of pocket....In dead of night, couldnt find keys.....Waited till light, went to get keys before they called police.