Everyone loves a good courtroom scene. We get lots of dramatic speeches and over-acting and Jack Nicholson reminding us that we can in no way handle the truth. But more than that, these scenes ultimately lead to Lady Justice being served. The bad guys go to jail.
Unfortunately, much of the time justice gets served only because a screenwriter twisted the law beyond recognition.
The Crime: Murder, Assault, Bootlegging, basically being a Mob Boss and Tax Evasion
The Ruling: Guilty Because Your Lawyer Says So
Kevin Costner's Eliot Ness is determined to break the stranglehold that Al Capone has on Prohibition-era Chicago. He assembles an elite team of "untouchable" (i.e. not actually corrupt) cops, and after a couple dozen people are killed, they arrest Capone for the capital crime of tax evasion, which today can get you made secretary of the treasury. But anyway.
Look, Kevin Costner!
When Ness discovers mid-trial that the jury has been bribed, he confronts the judge, who is also in Capone's pocket, and threatens to expose him if he doesn't do something. Instead of declaring a mistrial, the judge switches the entire jury with the jury from the trial next door, after the trial has already begun.
In a moment of panic, Capone's lawyer changes the plea to guilty, and the courtroom erupts as though all crime has just been wiped off the face of the Earth.
Hooray! We're safe forever!
Ever had to go in for jury duty? And the lengthy selection process? All that stuff happens for a reason. Juries are specially selected to avoid a conflict in the case being tried -- hell, Capone's second cousin could have been in the jury next door for all they knew. That's why a judge doesn't have the power to place a jury that the lawyers haven't selected or interviewed, let alone do so mid-trial.
But this point becomes moot minutes later, when, seeing that the evidence is stacked against them, Capone's lawyer switches his plea to guilty. The court erupts, cheering, while Capone punches out his lawyer and is then seen in the background being led off to jail screaming, "Is this justice?"
Well, no, actually.
This is Sean Connery.
The whole point of the scene seems to be that Capone's lawyer switches sides and pulls the rug out from under Capone. But in real life, a court can't accept a plea without a defendant's verbal consent, no matter what the lawyer suddenly announces.
"Oh, and that DUI I got charged with last week? He's pleading guilty to that, too."
The lawyer works for the accused, after all. Which means that instead of the court celebrating like they had all just won the lottery when they hear the guilty plea, Capone actually could have just fired his lawyer, had him killed (not necessarily in that order) and then stuck with his not-guilty plea and bribed the next jury, too.
The Crime: Murder
The Ruling: Not Guilty by Reason of Awesome Acting Abilities
In Primal Fear, Edward Norton viciously murders a priest, stabbing him 78 times and cutting off his fingers, and then runs away covered in his blood. Richard Gere is a Chicago defense attorney who goes apeshit over the awesomeness of this and takes Norton's case. They submit a plea of not guilty, but while investigating the case, Gere finds out that Norton totally did it, but he also appears to have multiple personalities, so he should be all set to go with an insanity plea.
Pleading insanity is the duct tape of legal defenses.
The only problem is that he isn't allowed to change the plea in the middle of the trial, which means his crazy, guilty client is going to be found just plain guilty, without the added fun and lenient sentencing that comes with the crazy part.
The only solution Gere can come up with is putting Norton, who is soft-spoken with a polite stutter, on the stand in his own defense. When the tough-talking female prosecutor lays into Norton about murdering the priest, his alternate violent personality comes out and Norton attacks her, proving he's crazy.
After Norton is arrested yet again, the judge calls both lawyers to her chambers to discuss the case. After Gere assures her that Norton is actually crazy, she decides to dismiss the jury, declare it a bench trial, find Norton not guilty by reason of insanity and remand him to a mental institution to decide how long he'll be committed. And then comes the twist ending ...
... In the final scene it is revealed that Norton was faking the whole time: There was no alternate personality and he is simply the world's greatest actor. The cold-blooded serial killer is his true personality, and the soft-spoken stutterer was all an act.
The best part is he can't be tried for the same murder twice (that'd be double jeopardy), so once he checks out clear at the mental institution, he'll be back on the street. Gere is both mortified by this and insanely jealous of Norton's acting ability since, unlike himself, Norton clearly has enough range to play characters who aren't lawyers.
Psychology can be an inexact science, sure. But still they tend to, you know, actually have experts test people before declaring them insane. Instead of subjecting Norton to testing by any kind of court-appointed psychiatrist and waiting for a report from an actual expert, the judge just decides that "yeah, he seems pretty crazy" and sends him off to the loony bin with no questions asked.
Hugs all around!
And keep in mind, we as an audience have been seeing Norton's split personality emerge slowly throughout the film, and we know that he switches from mild-mannered kid to crazed sociopath. But the judge sees only one violent outburst in a courtroom from a defendant who is on trial for a vicious, bloody murder. Which is kind of what you'd expect to see.
And yet within moments, she has him declared not guilty by reason of insanity, partly because Gere assures her that Norton is indeed insane.
"Who in his right mind would do this? Not guilty!"
There was no reason for the judge not to wait for him to be tested to make her decision, just in case the guy's attorney might have been lying or even mistaken, since he's a lawyer, not a psychiatrist. Or she even could have declared a mistrial and allowed him to be tried again with an insanity plea to begin with, but apparently she's very busy, as she is seen going home immediately after making her decision. She doesn't have time for shit like this!