Young couple goes on van tour of US, boy comes back with van - no girl

I think that right now him murdering her is no more likely that some type of accident (a fall or drug overdose), and him just reacting poorly, then continuing to act poorly as he realized his poor reaction just made him look more guilty.

The guy is definitely not innocent. and he should just come clean about whatever it is. He's not going to escape punishment by acting guilty, that is for sure.