Deathnote 3 by Tsugumi Ohba & Takeshi Obata

Very cool manga about a guy who picks up a death notebook--like you write someone's name in it and they die. So him and this demon type thing from another world go around killing people, but only he can see the demon. But the thing is he's killing mad people thinking he's doing a service to society by killing criminals. Now the police are looking for who's behind all that death. -Rachel Wagner