So assuming RA is BG and the killer...
He backs his car into a spot next to the old CPS lot and starts walking the trails sometime shortly before the girls are dropped off, 1:30 according to him. He passes some people, including juveniles, glaring and not responding to them. He is already on the bridge when A and L are walking the trail toward the bridge. He's not in L's photos from the bridge, so apparently he is somewhere nearby and out of view. The girls cross the bridge and by 2:13, he is behind A on the bridge while L films. One of the girls notices a gun, he approaches them, tells them "G...DTH," they go down the hill and the video stops. At this point, we don't know the sequence of events, but during the next hour to hour and a half, in some order, the girls clothes are removed and end up downstream of the CS, they cross the creek, they are killed, moved, and staged. RA leaves an "odd" crime scene, with signatures, and no obvious motive (according to RI). An unspent bullet ends up between the bodies, RA exits the CS, with some sort of trophy, muddy and bloody, and walks 300 Rd west, back to his vehicle at 3:57 pm.
It's all very bizarre to me.