The newspaper did say several men were found "drained and in debilitated condition", which is pretty unclear as to the specific damage done, but seems to be nonlethal. It could even be fairly minor, though it sounds at least considerable. Still, that's hardly sufficient justification to commit mass murder like that. And, uh, goddamn that panel showing it was a punch in the gut.
Seriously, what the hell is this shamelessly trashy manga doing, being so good like this? I love it so much.