If the path they took from the bridge was as GH shows in the video, ...why cross the creek??? It's hard to think like the perp but something made him take this risk. There was a chance of slipping etc.. Did he know that it was owned by an older man that drank and most likely wouldn't come down to the spot where the bodies were found?
Why there?
Imo...one possible scenario is:
The girls tried to get away from BG and/or possible accomplice by running away down the small hill and across the water. If BG chased and caught up to the girls as they were trying to climb the much steeper hill toward cemetary, he may have ordered them to come back "down the hill". They could have complied and ended up right at the spot where the crimes were committed. Maybe BG caught up with just one of the girls on the other side of the creek. As she was under his control with a weapon, he may ordered the other to come down the hill or he would harm her friend.
imo, moo