Once you go "down the hill", there's no going back up it. Literally.
In all the sleuth and what have you videos of the spot where they were forced down that hill/berm, I've never seen anyone attempt to walk up it.
The girls were caught by surprise at the end of the bridge, with their only "escape" being a run through somewhat-dense vegetation into the wooded area beyond the SE end of the bridge, the former railroad right-of-way. MOO, BG grabbed one of the girls and subdued her, which might explain why we have audio of the initial abduction. Even in a pocket or in Libby's hand, the voice of the killer could have been picked up.
Another hunch I have about the abduction is LE has a lot more audio, note they released "Guys...", two years after the murders. Gee, what was happening when he said that? Right after? What else was said? What orders were given?
I'm of the opinion there's a gap in our timeline, here, for the audio:
1. "Guys..." or "Guys?...", followed by him grabbing and subduing one of them, maybe tying them together, etc.
"Guys", he gets their attention while Libby's phone is comfortably held in her hand.
2. He orders them "...down the hill...". This part of the audio no doubt was terribly garbled, and had to be cleaned up by audio experts. Was the phone more firmly clutched in Libby's hand, inside a pocket maybe, or ??? There may have been a fairly decent amount of time between "Guys", which sounds near crystal-clear, to "down the hill", which sounds a little more distant, and definitely garbled. Many seconds? Half a minute? A lot was happening in a short period of time.
You're in the gorge, now. Trapped. Your choices on that road/driveway are to go either way on it, or further down into the gorge down another incline, to the flat area.
But you're still stuck in the gorge. In this specific case, maybe even tied to your friend.
The section of driveway under the SE end of the bridge has a dip to it. So either way on that driveway, at some point you're going up hill, either to the house, or C.R. 625.
Up hill is a barrier and slows people down, especially people in an unfamiliar area where they may not know where up hill leads, or can't see where it leads. You can't see the house, any house, from that spot in the gorge. They could see it when they crossed the creek if they'd turned their heads to the right, but go ahead and scream. Nobody's home. They had to walk approximately 450 feet or more to the edge of the creek, at that spot BG already has lots of cover and concealment, to use a term we used in the USMC.
BG knew nobody was home. How did he know this? Did he know the owner is a snowbird? Did he know the routines of the family member or members who would stop by to check on the place?
BG also knew the terrain. People could have been there many times beforehand, but never gotten used to the terrain within the gorge. IMO he knew general distances, times to walk them, etc. Difficulty. What kind of foot wear to wear. Indications from witnesses during the search and Libby's sister show that one of Libby's shoes came off, my guess would be the suction of the muck on the north side of Deer Creek pulled the shoe off.
BG's shoe or boot never came off, not the entire time he was out there that day. BG had it all planned out, nothing would stop him from murdering that day.
From "down the hill", at that very spot, the girls could have looked around and been disoriented and had no idea where they were. It's a completely different world than on top of a bridge 30-60+ feet up. IMO they most likely had never touched that spot, like most people who have been to Monon High Bridge and walked across it. Walked across it for years. You might walk across it for many years, despite it being private property and hazardous, but you get to the end, turn around, and go back. No reason to go down the hill, and besides, once you go down it, now you have to go back up it, and back across the bridge.
Why? It's private property down there, and besides, what is there to do once you get down that hill?
Who, as a perp, would know this? Someone who has been there before many times, and has observed people walking across the bridge, and walking the trails. Every serial killer I've studied, studies his or her prey, or just people in general, looking for people to victimize. They also look for what else?
Others in the general area, and what their typical behavior entails. Anyone who looks like a LEO or could "play the part", people who could be armed/could defend themselves, and other people who might "get in the way" of their fantasy or fantasies.
This guy had it all planned out, MOO only I bet he planned it months in advance, not hours, days, or even weeks beforehand. Months.
I had to bend my head around the bends in the creek early in the case, to get a feel for the area and how those bends probably helped our perp. The vegetation along the creek, combined with the bends, the 'blurred background' one would see in a wooded area with hills, or a valley/gorge, etc., offer perfect concealment. One cannot see the CS from the bridge, even in February. He planned all that out.
He planned it well beforehand, then he came back.
Why did he come back? The elements of that gorge, and the fact that IN 25, which opened in 2014, offered a quick escape route away from that immediate area, and he didn't have to drive past busy, open businesses and other places where people would have seen him driving by, turning a corner, etc. Andersons wasn't even open, and they have lots of surveillance at that terminal complex when they're busy.
JMO