I've heard plenty of prosecutors joke about it being more fun to convict the innocent, but it's nothing more than a joke. There is plenty of hard evidence connecting Casey to the murder of her daughter, starting with the fact that her car smelled like a dead body had been in the car. If Casey, who continued to use the "dead body" car after the smell was noticed by friends, was not responsible for putting her daughter in the trunk of her car, then who?