Hikers. My bet is they were all hikers.
A clue of sorts, but not much.
Maybe the killer is a local guide, or other person well known — and possibly well liked - on the many trails that much exist in the area.
Could be. But, most ‘hikers’ wear hiking boots. Running shoes don’t have much ankle support. The running shoes don’t keep dry like most decent hiking boots. Especially in the NW, running shoes would be a last pick. But, that also could mean they were inexperienced in such things and got into trouble.
Doesn't make sense for several reasons. Hikers don't usually hike across the bottom of a lake or river.