Thanks for asking! I've come to think it might be more like this:
-> They are at the south side of the bridge when he reaches them (did he pass them on the bridge going north and double back? I don't know).
-> He manipulates or intimidates the girls into compliance (no screams heard, doesn't seem like they ran from him).
-> But does that mean they went Directly DOWN THE HILL at the left side of the south end? Or did he march them a little ways away from the bridge and then they're down the hill?
-> Possibly they didn't go with him right directly off the south end like we think? Maybe they decided the best way away from him was to cross the creek on their own, and get back to the place where they were to meet DG? Sure, the crime started at the south end of the bridge. That could be as simple as BG appeared in the video there. We don't know where he / they were when he says words to them (do we?). We assume its that hill immediately to our left at the south end, but is it??
-> Maybe the girls crossed the creek at a decent clip hoping to evade him? He catches up and that's when he attacks?
-> OR: maybe he planned to take them to that abandoned house at the south side and attack there? But the plan changed because maybe they ran? Or one ran? We don't know. We assume he marched them down that hill and to their deaths, but that might not be how it happened, and I bet police know a lot more than we do.
It will be interesting to see how the girls ended up where they were found. If they ran from him? If they were heading back up towards the cemetery when he caught them? We just don't know.
-> Also, I think he went to the house on the south side and hid in an outbuilding there until he could escape in the darkness (however long that was for him). I don't know if he used the cemetery route to escape or not. But it won't shock me if he had a quad or car along that private drive and just cruised out when all was done.