Murder as a mean to obtain their posessions isn't unheard of nowdays in policed societies and murder for fun, thats completely heard of across the world right? Also this isn't some crumbling civilization, it's gone, there is no government to keep people restrained, that being said the ability to reclaim an area (albeit temporarily would be cool). Finally please don't compare 9/11 to an disaster that killed over 50 million people, especially in the context of civilization ending events.