Leave No Witnesses

"Team Leader: There's no sign of Dredd. He appears to have survived the crash. Judge Griffin: You are in error, Capture Team. No one survived the shuttle wreck. Understand? Just find Dredd! Leader: The pilot, sir. He's alive. Griffin: No one survived the shuttle wreck! Do I make myself clear? Leader: Yes, sir. [Shoots the pilot]"

- Judge Dredd

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.

Oh, by the way, if you're a Mook and you've been ordered to kill all the witnesses, one thing to keep in mind: As far as your boss is concerned, you're a witness, too.

A specific case would be Killed to Uphold the Masquerade. People who are Trigger Happy may jump to this solution a bit more readily. Contrast with Leave No Survivors, where you're killing everyone just out of general bloody-mindedness (or hatred.)

Anime and Manga

 * It's mentioned a few times that Golgo 13 will kill any witnesses to an assassination as a general rule. (Usually, though, there aren't any.)
 * Ophelia, from Claymore is big on this. Claymores aren't allowed to kill humans, but Ophelia is more than a little Ax Crazy, so she tends to get carried away when she fights. Solution: Murder everyone who saw her.
 * In Berserk, Guts instinctively did this when he heard a witness after he assassinated Duke Julius on Griffith's orders. He realized too late that it was the Duke's young son, whom Guts empathized with earlier.

Comic Books

 * In Top Ten, Comissioner Ultima will have to destroy Neopolis to prevent word of her Xenite addiction getting out.
 * The Rourke family in Sin City usually ensure this when covering up the trail of bodies left by the two different SerialKillers connected to them; even going so far as to try to kill children or lowlives like Marv. Both of these targets end up being their own undoing, however.
 * In Asterix and the Secret Weapon, Caesar demands that no witnesses be left of the titular secret weapon (since it would not only be seen in Rome as dishonorable but also ridiculous). When pirates threaten the secret ship, the leader announces "Caesar said no witnesses, so No Quarter!" and just charges through the pirate ship, ripping it in half (which conveniently allows the pirates to survive in their rowboat since they didn't see anyone).

Film
"Waternoose: Get up! There can't be any witnesses. Randall: There won't be."
 * Judge Dredd, in the page quote. After a shuttle carrying prisoners to Aspen Penal colony crashes, a rescue/capture team is sent to locate Dredd, a convict on the flight. The Capture Team Leader reports to Judge Griffin; Judge Griffin spells it all out.
 * A similarly creepy exchange in Monsters, Inc.:


 * In Universal's 1932 The Mummy, when the renegade priest Imhotep is buried alive with the Scroll of Thoth, the slaves who dug the tomb are killed—then the spearmen who killed them are killed, so there will be no witnesses. (This sequence was incorporated wholesale into the 1940 Continuity Reboot, The Mummy's Hand.)
 * In Kill Bill, Bill and his squad kill everyone at The Bride's wedding, even "the colored fella playing the piano".
 * In the 1968 Italian movie Black Jesus, the Patrice Lumumba-expy is taken out to be shot along with two criminals. After he's executed one of the criminals says, "Don't worry, I didn't see anything". The executioner replies, "Yes, but you heard something" and shoots him when he turns to run.
 * The Mask of Zorro: When it's planned that the mine is to be blown up, its peasant workers (including children) were also trapped to prevent witnesses.
 * This seems to be an unwritten "rule" in low-budget slasher movies; the first time someone kills someone (even by accident) he feels he has to murder everyone who might be a witness, this often cementing his Start of Darkness, as he quickly finds It Gets Easier.

Live Action TV

 * In the Firefly episode "Ariel", the blue-gloved operatives come to pick up River and Simon from the Alliance police who've arrested them. When the lead policemen mentions that they'd talked to the prisoners, the operatives kill every policeman involved in the arrest.
 * ...in the loudest and most gruesome way possible, which actually helps the prisoners escape.
 * Possibly subverted in Lost when Michael kills Libby.
 * Appears to be the Standard MO for Dead Larry in Burn Notice

Literature

 * The Doctor Who spin-off novel The Eyeless features an alien superweapon that turns out to be part of an extremely thorough attempt to remove all witnesses: not only did they kill the witnesses, they destroyed the entire planet they were on and then every other planet that could see that planet through telescopes or whatever.
 * Subverted in the first Dune; a search party was supposed to find and kill the two perpetrators and witnesses to Paul and Jessica's killing, but they were already dead when they were found...
 * Two "men's adventure" novel series by Joseph Rosenberger, The Death Merchant and COBRA feature characters with a very extreme moral compass who often follow the "leave no witnesses" rule to protect their identity. The lead character in Death Merchant has a policy of killing people who learn his real identity, friend or foe, and in COBRA the "heroes" even go so far as to kill local law enforcement to protect their mission.
 * In the third book of the Knight and Rogue Series the wreckers kill anyone who has even the slightest chance of having seen them. Michael is almost killed just for noticing them off in the distance while they're discussing plans.
 * Septimus Heap: The Port Witch Coven Witch Linda intends to throw Wolf Boy to the Grim after he's fed Lucy to it so that he can't spread the information, since she's read many detective novels. It doesn't work out.
 * In The Bible, Jacob's daughter Dinah is raped by a Schechemite prince, and her brothers kill him for it. They also kill all the other men of the city, and take the women and children as plunder. Some would see this as Disproportionate Retribution, others would see it as Combat Pragmatism; killing the other Schechemites leaves no men to avenge the prince (and in this time and place, apparently no women willing or able to take vengeance either.) Either way, Jacob worried that someone would take revenge on him and/or his sons for their action.

Video Games

 * In Ghost Trick, the murderous motive of the blue foreigners is to kill everyone connected to Temsik, so they are the only one who know about the meteorite's powers.
 * Joe Darke was a serial in the first Ace Attorney game. He hit and killed a woman with his car, then panicked and started killing everyone who was a witness.
 * The final mission of Hitman: Blood Money features Agent 47 reviving at his own funeral and killing everyone who saw him do it (including an innocent priest and a reporter), and, in the process, taking his revenge on the people who've been screwing him over for the entire game. The mission objective is given as the trope name.
 * Often an explicit mission objective in City of Villains.
 * In Warhammer 40,000: Fire Warrior the Space Marines sent to kidnap the Ethereal were ordered to do this.
 * In the Silent Threat expansion for FreeSpace: The Great War begins with a mission in where you have to cover up a skirmish that occurred between Terran and Vasudan ships by killing everyone who saw it.
 * In World of Warcraft: Cataclysm, the Goblins fleeing Kezan wind up in a firefight. The humans don't want witnesses, so they blow up the Goblin ship, leaving them shipwrecked on the Lost Isles.
 * Naked Snake gets told this early on in Metal Gear Solid 3: Snake Eater. Actually doing so is ill-advised, as it makes a later boss fight harder.
 * Committing a crime in The Elder Scrolls V: Skyrim gets you a bounty. Killing everyone who saw said crime erases it.
 * In The Godfather 2 there may be witnesses to your crimes. You can run away, intimidate them into silence... or just kill them.

Web Comics
"Redcloak: ...The exact details here need to remain between me and our god."
 * Jägers in Girl Genius discussed this topic. Dis is turnink into vun of dose plans...
 * Included in the difference between a good magician and an evil magician, as described by Master Payne.
 * In Blue Yonder, the team coming after the capes kills any civies in the area.
 * Redcloak from The Order of the Stick, when destroying the Resistance and retrieving Xykon's phylactery, uses monsters he summoned, allowing him to simply send them back to their planes. He also doesn't resurrect the hobgoblin spy he used, and is thankful that he died in the battle, or he would have had to kill him himself. Then he buries the location with an earthquake.


 * A few strips later, after Tsukiko discovers too much about Redcloak's manipulations, he takes control of her wights and has them kill and eat her. He then orders them to eat each other, and for the last one remaining after that to set himself on fire.
 * Right after this, he disintegrates the body of the hobgoblin who made a perfect copy of the phylactery and was killed by Tsukiko because he was in her way.
 * Vaarsuvius' use of the Familicide spell, given that it was casted to ensure that nobody related to the target in question would ever come seeking revenge. It would come back to bite Vaarsuvius in a practical manner much later.

Western Animation
"Lisa: It could be anything, it could be a mutant from the nuclear plant. Burns: D'oh! Fiddle-faddle, everyone knows our mutants have flippers. Oh! I've said too much. Smithers, use the amnesia ray. Smithers: You mean the revolver, sir? Burns: Precisely. Be sure to wipe your own memory clear when you've finished."
 * Spoofed in King of the Hill, where Dale tells Hank to dispose of the witnesses to a minor accident.
 * The Simpsons, when Lisa unearths what looks like an angel: