Most people take their phones everywhere so if BL did take off, and GP was sad and someone tried to console her. She probably would have taken her phone with her. So whoever hurt her could have had it and them mistaking Yosemite for Yellowstone even more likely. I don't want to give BL any more alibis but I would hate to find out that he hurt himself and he was innocent. Can you imagine how much that would compound this tragedy? I know it's stretch.