im not sure if this has been mentioned and it might be totally crazy but....
what if casey drove the body out of state? that would explain the god awful smell in the car, the need for extra gas, the reason no one saw her for days. she seemed so sure of herself when she said "caylee is in new york or north carolina." new york is too far. but north carolina? the anthonys must have mentioned it 10 different times. and then, if the body was found in NC, casey would look brilliant and believable - the imaginary nanny did take caylee towards the "mountains of NC" or whatever the hell cindy said....
i assume the police will have her phone records about this, so they can place her location, but i dont know.