Earlier is was suggested that the marks in the tree were caused by bullets.
I don't think he shot Gabby personally, because I believe shots would have been heard. There were other campers in the general area. Having camped in the wilderness myself, it is so very quiet.
No one has come forward that shots were heard, at least that we know of.
But...maybe someone has.
Gun shots would be normal as I think I remember it stated that elk is hunted in that area or nearby.