I think a tl;dr is needed. I read part 2, but only after a comment indicated I should. Gary Mathias seems to have been INCREDIBLY violent at times - to the point where I actually wonder why the other men were allowed to go with him. At the very least, Ted Weiher - it seems he was less high functioning than the others, based on descriptions of his actions. I can see him not even processing that something was going really wrong, which is tragic. :(

If Gary Mathias had anything to do with it, though, I don't think he was responsible for the deaths themselves - they sound like natural deaths as a result of being lost. But I do wonder if he didn't think they "had" to go where they did (he also had paranoid schizophrenia - maybe he thought they were being followed?), or if he didn't get violently angry to the point where they exited the vehicle and things escalated horribly from there.