Assuming RA is the killer...
How does one go from point A: having no criminal record, owning the same gun and living in the same community for over a decade, and walking the same trail system on a regular basis, to point B: parking at the trail, walking with a mission to the bridge, waiting around the bridge for around 10 minutes before following two girls across the south half of the bridge to kidnap and murder them?
If something had simply triggered him to kill at random that day, why those girls? The witness who saw him on the bridge, only 50 feet away...why not her? He crossed the entire bridge in less than 5 minutes (somewhere between 2:07 and 2:13), so why didn't he cross 50 feet and force that lady into the woods at gunpoint when nobody else was around, not even the girls?
IMO, RA might have gone from point A to point B because this was not a random, triggered attack, this was a personal, targeted attack. He seemingly spent quite a bit of time with them, behaving oddly and leaving behind signatures of himself. I've been wrong about a lot of things, and this could be another, but it's my feeling as of today that this was intensely purposeful to him. JMO.