What would be the silliest thing a murderer would do? why, he would appropriate the van they both were driving around in , and for reasons that at this point defy any rationale whatsoever, drive that van from Jackson , Wyoming, to Orlando Florida. 2500 approx.. miles, not klms.. about 3800 klms..
He wasn't going back to a job, or a spare girlfriend, or an inheritance, or a previous appointment, arrangement, a job interview, whatever. He had not finished the journey , there was plenty more of the USA to hoot around in.
Mile after mile, exposed on the freeways and highways, getting meals, using facilities, obtaining fuel.. using the bank..
How did he intend to explain the absence of Gabby ? and his apparent ownership of the van? and why had she turned the van over to him? where was she?.. He must have figured it out that these questions would be asked, and had to be answered, surely?? He is 24, not 14.