I'm back near where I started.
Scenario:
BG is driving west on W 300 N and sees two girls dropped off. He goes around the bend and parks at the CPS building, then gets on the trail to catch up and follow them. (Alternately, he's already on the trail) The girls start over the bridge, and eventually, so does he.
This is where I break off into two ideas. I'll go with the one that puts BG with the girls the least amount of time. The girls decided to wait around under the bridge in the wooded area for BG to recross and be gone. He does recross, but is still yelling down to them, or is stopping and watching, or otherwise acting strangely. At this point they basically have no choice but to either go back via the bridge where the weird guy is, or cross the creek to get back to their ride. I think they cross the creek.
BG gets to the north end of the bridge, checks for people coming, and goes off into the woods to corner the girls. He gets to them up the hill from where they were found, orders them back "down the hill." From here I'm guessing things get very rough, very quickly, and is over in a matter of a few minutes.
(The alternate scenarios, in my mind, are that they all cross back over the bridge (various possible ways), he orders them into the woods on the north end, and marches them to the location he killed them. Or, he waits around on the trail and the girls try to avoid him by going through the woods, but he corners them). These are my secondary options only because it puts BG with the girls for a longer extent of time.
Again, I have multiple ideas on how BG gets back to his vehicle. Either he walks the woods/trail and gets there, but has a problem (as I posted yesterday with the car key scenario), or there are now people on the trail when he's in the woods coming back, so he hides out for awhile (or takes a different route) and doesn't get to his car until much later.
I think in the encounter, BG's hat gets knocked off, which in turn drops shed reddish brown hair. He doesn't leave the hat, but the hairs are left behind. If the hat is his, they're probably his hair. If it's not his hat, it could be the owner's hair.
I also think the YBG witness saw something related to either the vehicle or the CPS lot (or both).
Just tossing around ideas.