Sunday night was accounted for, by his dad. It's just that a lot of people refuse to believe him. Maybe LE does, though.
Just to clarify... I have seen posts that clearly, (to me) state he could not or would not have hitched a ride. As if they know it is not a possibility. I am just saying that it is, IMO. No offense to anyone here, I know it's hard to explain the lack of activity on his phone, but explanations for that have been offered as well. Yet it's quickly discounted because it doesn't fit the theory.
What if Dylan's phone just died that night, and he didn't have a charger? Thought he packed it, but not there. Or the battery wouldn't take a charge. So he was tired and went to sleep, after Dad said he would pick up a new battery the next day. He didn't remember his friends' numbers off the top of his head. Got up after his dad left and said, 'heck with this, I'm just gonna hitchhike over there.' Took his backpack because he planned to stay a couple days. Took his fishing pole, too. Somebody came along who he thought he recognized, maybe barely knew, and.... something happened.
Pick out the holes in that scenario all you want to, I'm not even calling it a theory. I'm just saying, it's possible. Maybe not probable, but then how much ever is?