I have a few random things built up in my brain-
1. I do NOT think he flagged her for help. Everything about this guy says that he feels real joy and power from the ambush. With RG, he passed her, turned around and rammed her from the back. I think that is exactly what happened. This guy was not confident enough to sit on the side of the road and hope a cute girl passed by and stopped to help his creeper looking self. I do not think that happened at all.
2. The boards they took with holes and the hook eye bolts (I might be calling them the wrong names). That seems to me to go together. This dude had wood with holes drilled in that were holding bolts that he had restraints attached to. He's disgusting.
3. So, why all the digging? I have followed many cases, but I am not sure I have followed any that went to digging so quickly. Well, I take that back- that husband and wife that were killed by their "friends" over a fight over drugs and they were buried in friends back yard. Arizona, I think. The started digging almost immediately, but they also found them in there! So, why all the digging in the barn so quickly? They must have thought something was there. And did they find it? Maybe they were digging out the room, but I cant imagine wanting to destroy that so quickly.
I had something else, but I cant remember right now.