Playing devil's advocate here. Let's say BL is either apprehended or turns himself in. A well known defense attorney replaces his current, ineffective council. They go to court and the new story is...
Brian and Gabby, as they had done so many times before, kissed and made up. He decides to go off on his own to hunt berries or camera shots and leaves Gabby near the van to update the website. Upon his return, Gabby is nowhere to be seen, so he peers through the thicket to see if she's exploring the creek bed. Suddenly, he sees two men menacing and beating her. He panics, throws on his backpack and beats it out of there. He's so terrified that he offers $200 to the first campers he meets to get him the hell out of dodge. He's conflicted, he doesn't know if she needs help, she's dead, whatever. Once he reaches Jackson, he develops a conscience, decides to hitch a ride back to the vicinity of the van, stealthily works his way back to the crime scene and finds the assailants gone and Gabby dead. He KNOWS the Moab PD has him and her together battling. He KNOWS he's the last identifiable person to be seen with her. He panics further, leaves her dead body out in the open, grabs the van and books for Florida where he withholds this info from his parents - only relating that something terrifying happened out on the road and he might have either been followed or is in mortal danger. They spot him $5K, drive him to parts unknown and tell him to lose himself.
Johnny Cochran once said, "Sometimes, the one who wins is the one with the best narrative."
Reasonable doubt? Does Brian walk?