If Christine can't be believe then he may not even be missing but may have told her he was leaving with a friend for a road trip and don't ever expect him back. He might have even said he was leaving and moving in with a new girl friend and wanted to keep the car but the police took it.
At some point we have to believe that some facts are true because if we don't then THE ONLY fact is the car was found with NO evidence in Federal Way.
We also can't just discard the ones that don't fit with what we want to be the truth. Although I'm not sure anyone has a clue as to what they want as the truth.
ETA Oh and he also decided not to work any more but that could just be so he wouldn't have to pay child support.