Condemned Criminal Origins - As you proceed forward. An enemy will jump out at you. Shoot him in the head for an instant kill. If you are trying for Achievements you may want to fight only with melee weapons. You can make a gun into a melee weapon by pressing the RB button. I did shoot the first few enemies with a gun in this chapter, and still got the Achievement at the end of the game. Maybe the first few enemies don't count since they are kind of a tutorial?