Okay, here's my newest crazy variant of my other idea.
I can't get past the idea that the girls might not have wanted to be on the bridge with BG, either following him, or with him behind them. So I'm back to considering the girls choosing the woods, but maybe with the idea to hang out just below the bridge until he hopefully crossed back and left.
You can tell from the photo that if you were in the woods below the bridge, when the leaves are off the trees, you're visible from the bridge, especially in pink and tye-dye shirts. So maybe BG was acting weird, walking back across the bridge, but obviously watching them. With him on the bridge, they are virtually trapped.
The girls decide he isn't going to leave them alone to come back up and recross the bridge, so they cross the creek to avoid him. They would be scared, IMO, and wanting to get to their ride.
I also then wonder if once they're across the creek, they can see BG in the woods off the north end of the bridge, heading towards them. At this point they might head towards the cemetery, or whatever, but BG intercepts them, makes them go "down the hill" somewhere nearer the spot they were ultimately found.
In this scenario, BG doesn't really march them anywhere other than very close to the creek and crime scene. Much less time with him "controlling" them. For their last 30 minutes, a lot of that is them knowing they're being stalked? Just a thought...