Almost all criminals are hunters in the sense that they are predators, looking for victims likely unable to defend themselves, locations where they won't be detected, etc. But none of that requires a firearm, let alone multiple clips (magazines), etc., or having recently been on safari. In fact, as has been widely speculated here, a firearm was likely used only to control the girls, not for their actual murders, because (1) the killer wouldn't want noise to attract attention, and (2) most sexual killers, if that's what this was, favor more personal methods of killing. An AR, and rifles in general, would be a poor choice in this case because of their extremely loud report (much louder than a handgun).