Hitman is noun, verb, adjective, pronoun, and interjection. Hitman will kill you. How? Doesn't matter, he'll find a way. Witnesses? No. Nobody has seen Hitman. Not even you. You've just watched this video right? Well then Hitman is probably already in your room pouring ether on your unmentionables. How do you defend against Hitman? You don't. Unless you have a wheelchair. Thats when things get interesting.
*Kinda spoilers at the end which I just have to say is the all time best ending to a game I've ever played.*