So are you saying that you think CM was in EA's trunk all the way to his home at 5:30-ish, and then he went E from there, maybe a long round-trip "road trip" in those next 4 hours, to get rid of her or her body? If we go with that theory, she then can be anywhere in a 2 hour drive radius, and a search would be pretty much an exercise in futility, wouldn't it?
One thing that might be worth exploring. Do they have a way to see how much gas he got on Sat morn, and then look through his bill and see when he last filled up before then? Gas usage, if they can even get a rough approximation, can somewhat limit the possible distances in play.