During the mission Curtains Down it is possible to kill the singer in front of a room full of people without being shot at. If you have the real WWI pistol then enter the dressing room of the executioner while he's on stage and shoot the mirror twice with any gun. Wait in the closet until he enters then leave the closet and sedate him (note: if you do shoot the mirror first, he will spot you)take his outfit but not the prop gun. Walk back on stage and draw the WWI pistol. Then wait for your cue to shoot him and when you do, he will die and it will still count as an accident.

Note: If you shoot him too early or too late, you will be shot at.