Perhaps Ben and Gunny were both transported up to the logging area by someone Ben trusted, maybe the evil one offered to show Ben caves, old mines, and shacks on the mountain by horseback? Up on the mountain Ben unloads and gets on Gunny, his back is turned, boom, and Ben falls. Gunny is upset by all the sudden commotion, the killer cannot catch her in his hurry, so he loads Ben in the horse trailer beside his horse, and takes off, leaving Gunny on the logging road. Gunny is from Wyoming, and if trailered in, could be confused where 'home' to return to, is. This ambush could have happened near a big log landing (logging truck loading area) where the killer's truck and trailer could be turned around.
Maybe the killer is capable of killing a human, but cannot shoot a horse? In a WS case in Ohio, 8 adult family members were shot dead in bed in the night, but 2 children and several dogs at the homes were not hurt. Or he hopes when Gunny is found, or makes her way back to the ranch, it will be simply assumed Ben was fatally injured during a ride somewhere on the big mountain. Perhaps the reason the police are asking for any cam coverage is they are certain that Ben and his horse were taken up that mountain by someone, and they had to be on and near that big busy highway to do it. Are there highway traffic cams in the area?
Was there minute blood spatter of Ben's on Gunny's saddle, reins, Gunny? Hopefully some clue was left showing Ben was attacked in the saddle. Maybe the person with the trailer will not willingly surrender it because there is blood evidence from Ben, and no matter how much it is scrubbed Luminol will glow? jmo