It was just any other day, another testament to the mundane dreary lives of the living. No one was prepared for their coming, how could they be? They entered the bodies of the living, transforming them into blood thirsty monsters, all in an instant.
What about a 'criminal' society with distinct laws - for stealing, the larger the value of something stolen, the less punishment the courageous thief recieves (but must return it of course). For this pirates(?) caught petty thieves deserve to be punished harshly. If you take, you better take a lot.