A particular subversion of a Kangaroo Court
. There's a hidden malefactor; you need to draw him out, either to reveal him or to have sufficient evidence against him.
One way to do this is to engage in a Decoy Trial. You initiate a false charge against a defendant you know to be innocent (whether or not you tell him ahead of time depends on the nature of the problem and the defendant).
You then move forward with the sham trial, observing closely for people who are 'pushing' the case and/or evidence you know to be fake. Or you "arrest" or "convict" the "perpetrator", and watch the real bad guy come out of hiding.
Obviously, any evidence gained from such a fake trial is very very dubious, and, in Procedurals, expect drama about whether or not it will be valid in a later, real trial.
The "trial" need not be an actual court case; preliminary stages, such as investigation or arrest, can be faked for this purpose.
- This happened to the Barry Allen version of The Flash at one point when he was put on trial for killing a supervillain. The trial was a decoy on both sides since another villain was manipulating the prosecution while Allen's wife was manipulating the judge.
- In The Krytos Trap, Rogue Squadron member Tycho Celchu is on trial for treason and murder. After several late-occurring events, including the murder victim's return from the dead, and the Super Star Destroyer Lusankya escaping from Coruscant, one of the judges (who is also the leader of New Republic Intelligence) reveals to the other judges that he knew Tycho was innocent of the crime the entire time and the trial was really a sham to flush out the real traitor. (Though the judge acknowledges Tycho might still have been an Imperial agent, and took steps in the event that that was the case—which, thankfully, it wasn't.)
- At the end of Malevil, Emmanuel is marched into La Roque by Vilmain's defectors as a "prisoner", with the late-Vilmain supposedly following in a few hours. Fulbert puts him on trial for imaginary crimes with the intent of condemning him to death. Emmanuel wanted him to publicly implicate himself as being in league with Vilmain, which Fulbert gladly admits to, believing Vilmain's killers and rapists to be a Necessarily Evil and instrument of God.
- CSI had an episode where they "investigated" a "crime", in order to draw out the perpetrator of an identical crime. It was called "reverse forensics," and the show went to a fair bit of effort to paint it as extremely controversial, to the point where getting caught doing it could cost those involved their jobs.
- Law & Order: Special Victims Unit also had an episode featuring one of these, which was a sting operation they set up to catch a judge who was taking kickbacks to send juvenile offenders to a particular institution (regardless of guilt). Stabler impersonated an angry father who offered the bribe, Agent Huang impersonated the defense counsel (since it was the FBI's jurisdiction) and a friend of the Victim of the Week played the defendant.
- In Dollhouse, Boyd allows and even contributes to the investigation against Victor to see if he raped Sierra, ultimately signaling for him to be brought in. This is done so that the real culprit Hearn, will be confident enough to rape Sierra again, and Boyd can catch him in the act.
- Near the end of an episode of Columbo, Columbo "frames" the perpetrator's son (fake evidence reported, fake witness against him) to get him to confess.
- JAG: The episode "Defenseless" has a female Ensign in the U.S. Navy killing the Turkish military attache in Washington. To convict the perpetrator, murder charges are brought against the Ensign who, unbeknownst to everyone involved in the trial, is the fake identity of an officer with Naval Intelligence, and evidence is purposely stacked against the ensign to maintain US-Turkish relations. In spite of this, the Ensign's defense counsel Harmon Rabb, manages to get her acquitted...
- Ace Attorney: Wendy Oldbag in case 3 of the first game goes through this, in order to buy some time. It's played for far fewer laughs in the final case of Justice for All.
- In the final case of Ace Attorney Investigations a variant is used when Lang accuses Franziska von Karma of murdering DeMasque II so he can get permission to search the crime scene, the office of the actual murderer.