You don't need to try and convince me, I never thought there was anybody hidden in the trees to start with. These girls were either followed and tailed to where they were eventually found, or the perp was lying in wait along that trail for the right victim to walk along. Somebody was going to be a victim that day. If it hadn't been these two girls, it would've been someone else, supposing that everything lined up right.
Stranger on stranger crimes are the hardest ones for the cops to solve, but out-of-town stranger on stranger crimes mainly go unsolved, unless there is a DNA match. I tend to think it's a local because of where the girls were found and how isolated it was. It's also possible the girls were deliberately steered in that direction by the perpetrator. He may have literally scared them down the trail by simply walking along behind them.
I really don't believe that though. Why ? Because he disarmed them so quickly and quietly that nobody heard any screaming, yelling, scuffling...........nothing. If he had been making them nervous in advance, neither one of those girls would have let him get close enough to grab them. To me, this is more like a guy rambling out of the woods, pretending he is lost and asking for directions, then clubbing one of the girls over the head with a huge branch, and then shortly afterwards having his way with the other one. You know, similar to the old, "Have you seen my dog?" routine.
There are still a huge amount of unknowns in this case, such as whether or not one or both of the girls was actually communicating with someone online, who they texted on their phones prior to this, who was on their friends list, who may have been following them online and knew they were going to be visiting the bridge. If none of that pans out, then this is most likely a predator waiting for the right victim to stroll along out in the middle of a popular teenage hangout spot.