Sorry for the double post. So, it's been over ten years now.
For four people to not turn on each other for this long (three now), they must all think they have something to lose by the truth coming out. I think all three know a lot more than they're saying.
I think they were all using drugs up there. Perhaps IR brought them which gives him more solidified reasons to remain complicit in the cover up. The missing teeth appears to be related to drug use—i.e. "meth mouth."
I think that some sort of accident likely happened while they were using. Possibly Deorr walked into the creek and drowned while they were all high—or he ingested drugs they were using and they found him deceased and they panicked and disposed of the body. Possiblly on the trip for tampons.
An abduction in that remote area is very unlikely. A premeditated murder also doesn't make sense because a camping trip in that location wouldn't be a good choice with such aforethought available. A wild animal attack is also unlikely because no blood evidence, boots, or clothing was located. I also doubt he wandered off on his own in that short of time with inclines all around him and no one noticing. So, that leaves an accidental death where they all fear culpability collectively.
Just my thoughts.