"Top of the hill" is a ridge line, which is a few hundred feet from the back of the cemetery. So there's no way to see anyone from up above, unless you're at the ridge line. Reason being is the distance from the ridge line to the creek, it's a short distance, as demonstrated by the image above.
I have a lot of land navigation experience from military service. To me, the top of the ridge is one corner of a triangle, the triangle being the cross-section of land between the ridge and the creek. The short side of the triangle is the drop off from the top of the ridge. Long side of the triangle is the land, to the creek. Hypotenuse becomes our line-of-sight.
As you walk up to the ridge, you see a clearing in the trees in the distance, then the creek, then the land as you're practically on top of the ridge. If this makes any sense. Let's say our searchers got this far, the top of the ridge line the evening of the search. Unless they had a really high-powered spotlight, they would not have seen anything out of the ordinary from the top of the ridge. I'm merely assuming they got that far, as they'd asked neighbors for permission to go on to the private properties along there. We need to keep in mind the search was centered around the bridge, and downstream.
I don't think BG had much in the way of concern for being seen by anyone, but as you stated there were risks, and he knew that. Which tells me he had to get the crimes over with, in a matter of minutes. This is MOO, but I think he incapacitated them, somehow, then murdered them.
Walk from the parking area to the bridge=roughly 8 minutes, probably somewhat less for most adults.
Walk across the bridge, at a leisurely pace, probably 5-6 minutes. BG probably crossed it in under 4.
From the SE end of the bridge to the CS: Considering time of year, I'd say under 4 minutes.
I don't see that many park users would access the CS and general area around it, via the path from the cemetery. It's private property, and that's posted. My hunch is folks use that trail for horseback riding, and for folks to keep an eye on their properties. In one video I've seen, a pick up truck is seen not far from the CS, obviously people keeping an eye on things after the murders.
This simple information tells me BG had been there before, perhaps several times before in the past. He had to have known that the bridge/park would have few users on a relatively mild February day, so people getting on to the trail from the parking area may have had a frequency of one or two every half hour or so. On, say, a warm summer day, it might be 8-12 users per hour. Something along those lines, is what I'm thinking.
I still maintain he was watching the bridge, concealed himself somehow, and was observing who was crossing, and whether or not they walked the entire length.
