I don't understand why you would want to kill the guards... All you're supposed to do is hide, kill the big boss, hide, and escape. Why should you unneccessarily kill guards...? That would make this game somewhat easy.
Holy crap! I got so frustrated that I finally pressed the "Help" button. In the section it gave me a valuable tip that is helping me so much...If you're a militia or a hunter, reload after every shot. I suggest everyone to read the help section..it actually HELPS.