Decoy Trial

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.

Examples of Decoy Trial include:

Literature

In The Krytos Trap, Rogue Squadron member Tycho Celchu is on trial for treason and murder. After he is acquitted, one of the judges (who is also the leader of New Republic Intelligence) reveals to the other judges that he knew Tycho was innocent the entire time and the trial was really a sham to flush out the real traitor.
- To be fair, he did say that he only knew that Tycho hadn't committed the crime he was on trial for; he might have still been an imperial agent.

Comics

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.

Live Action TV

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 and Order also had an episode featuring one of these.
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.

Video Games

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 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.

Western Animation

Inverted in one of the "Sideshow Bob" episodes of The Simpsons, where Bart and Lisa acted like they were doing this when Bob was on trial in order to force Bob to confess due to his ego.
- Variant when Homer and Bart (inadverdently) framed Groundskeeper Willie for carjacking. The guilt trip is piled high at his sham trial, until Bart and Homer confess to losing the car to a scammer. Turns out everyone else was in on the sham trial. Well, almost everyone.

Groundskeeper Willie: WILLIE WASN'T!!!

One episode of Roughnecks: Starship Troopers Chronicles had Razak brought up on charges, the trial then being interrupted by an Arachnid attack. The prosecutor was stunned when the commanding general reveals that the trial was a sham concocted by the general and Razak to reveal a security breach.