I also blame the parents. If either of my sons had the look in their eyes that this crazed individual had, I would know there is something wrong with him. If he is an introvert, has no friends to speak of, and looks like that, I would seek help for him. It might not stop it (nothing can), but I at least tried.
Maybe his parents are worthless and he had to live with grandma. I’m grasping, I know, but it’s a very possible scenario. Haven’t heard from the parents.