Sometimes you just can't afford to be seen. Everybody needs to believe you're dead. Or they saw you use superpowers, or now they know there are such things as vampires. Or they'll just testify against you and make you go to jail. So you have to kill everyone in the room. Or, possibly, the city. Similar to Shoot Everything That Moves, but that trope is more about the situation where everything you see is a threat. In this case, people would be more than happy to leave you alone, but that just doesn't seem to be an option anymore. Examples of Leave No Witnesses include: