I'm having trouble figuring out if this is a very stealthy criminal, or a very lucky one.
You have two physically healthy teenagers, hanging out at a favorite local hiking spot, with other people in the vicinity at the time. No screaming, no yelling, no running........nothing was noticed by anyone in the area ? There is a huge farming outfit and multiple residences within a rocks throw of where the bodies were found, they heard nothing either ? Sound travels a long way, especially high pitched screams, just think along the lines of a whistle. I know the trees and bushes will act as a sound barrier to some degree, but nobody else walking around in the area heard anything either ?
The bodies weren't hidden or buried, which means most likely it was a spontaneous hurried act. At this point it is impossible to establish if this was a prearranged meeting between the two girls and someone they conversed with online, or if it was a completely random encounter. LE will spend a whole lot of time in the next few days examining the girls computers and cell phone records for that very evidence.
I'm leaning towards a random encounter for one reason. The location they were found. Looking at the map, it appears to me that the girls were following along the edge of the creek bed. A totally normal place to hike. They were either tailed and followed to that location, or someone was already sitting off to the side of the trail when they walked up. Hiding in the woods, basically. Two young girls with no weapons, no boyfriends, and no adult supervision was the perfect target. I imagine a single female hiker/jogger was the intended goal.
If the girls planned on meeting someone there, they would have picked a landmark that is easy to find, such as one end of the bridge or the other. If they had met up with someone, chances are pretty good that other visitors would have passed by a group of kids at some point along the way. They would have heard them talking, laughing, cutting up, simply doing what teenagers do. It seems as if nothing was witnessed by anyone, except for the lady who claims to have seen the two girls together while crossing the bridge.
So is this a local ? Well............honestly...........how could it not be ? At least one of the girls cell phone was moving around town and pinging a tower later on that same day, so this isn't some criminal mastermind at work here, just a sadistic opportunist.
School was out.......the predator knew it..........lie and wait.......then pounce.