Insanity Defense

""Well, the work offered by organized crime must hold an attraction to the insane.""

- Dr. Jonathan Crane, Batman Begins

This is an affirmative defense in which it is claimed that the defendant in a criminal trial is or was unable to understand the nature or unlawfulness of their actions due to a mental defect or disorder, and thus not responsible for the consequences of those actions. "Insanity" here is a legal term, not a medical one, and the court decides whether it applies--though it will take the advice of medical professionals into account.

While the use of insanity as a defense has been known since ancient times, it was codified in English law by the M'Naghten Rules of 1843, and the United States adopted similar rules for its use shortly thereafter. Most countries in the modern world have some variation of the insanity defense available to criminal defendants. Some jurisdictions instead have "Guilty But Insane," where insanity cannot be a complete defense, but can be a mitigating factor.

In Real Life, the insanity plea is rare and difficult to succeed with. It is also a risky gamble, since it is an affirmative defense that requires the defendant to concede culpability in the crime in question and places the burden of proof on the defense to prove without a doubt their client was insane. Perhaps one percent of criminal cases even attempt an insanity defense, and only about a quarter of those are accepted, primarily if the defendant already has a history of mental illness. Furthermore, it requires expert testimony from a reputable psychiatric authority that the defendant was insane at the time they committed the crime, not just insane in general. Naturally, since the insanity defense is dramatic, it is used much more often in fiction.

A variant is "Temporary Insanity," in which the defendant is claimed to have been suffering from an "irresistible impulse" during the crime, but is now sane. Thus, they can be released immediately, rather than being incarcerated for psychiatric treatment. This defense was first used in the United States by U.S. Congressman Daniel Sickles of New York in 1859, after murdering his wife's lover. It was most prevalent as a defense during the 1940s and '50s.

Along similar lines, the "Extreme Emotional Disturbance" defense argues mitigating factors compromised the defendant's ability to think rationally. For instance, a man who shot his wife after catching her in bed with her lover could argue his emotional state at the time makes him guilty of the lesser crime of Manslaughter and not 2nd degree Murder.

Since someone who has been declared "Not Guilty By Reason of Insanity" is incarcerated for psychiatric treatment until they are deemed no long a threat to themselves or others, this can result in a longer loss of freedom than a normal jail sentence would have caused. Because of this, a defendant has the right to insist that this defense not be used in their case. This has not stopped some defendants -- both in fiction and in Real Life -- going for this defence under the mistaken belief that a plea of 'insanity' means a cushier time than a regular jail sentence. Also, in some jurisdictions, such as the District of Columbia, a person found not guilty of a sex crime by reason of insanity must register as a sex offender, as though that person had been convicted.

A "Catch-22" effect can be noticed with many juries--if the defendant is capable of understanding that an insanity plea would be a good idea, then perhaps they're not legally insane. (As insane people typically don't know they're insane - note emphasis on typically, since some actually do know there's something wrong with them.) This is in fact closely related to the original ~Catch-22~, the dilemma discussed in that book that a serviceman who requests a discharge for insanity must be sane enough to think to do so.

Another use of this trope common in fiction is for a floundering attorney to switch to an insanity defense as a last resort, ignoring the real-life procedural steps needed for this action. It almost never works, just emphasizing how doomed the client is.

A related concept is fitness to stand trial. This is often confused with the insanity defense, particularly since they often apply to the same people, but fitness to stand trial says nothing about their mental state when they did the crime. It's about whether their current mental state allows them to understand the charges against them and conduct an appropriate defense. For example, there was one guy who was clearly responsible for the crime he did, but while awaiting trial, he got brain damage from a suicide attempt and became unfit to stand trial. Rather than going to jail, he went to a care facility, and if he ever recovers enough he will stand trial.

Another concept related to insanity, although rarely seen in media, is diminished capacity. Diminished capacity is a claim that the defendant was unable to form the mental state (intent, recklessness, negligence, etc.) required for their action to be a crime. Because diminished capacity is not an affirmative defense, but rather the negation of an element of the crime, the burden of proof remains on the prosecution. Additionally, a successful diminished capacity defense results in a verdict of "not guilty", rather than "not guilty by reason of insanity", so the defendant is not incarcerated for psychiatric treatment (unless the state begins civil commitment proceedings). As a result, diminished capacity tends to be preferred to the insanity defense in jurisdictions in which it is allowed (although the two can be, and often are, combined).

In the United States neither psychopathology or a personality disorder is generally accepted as grounds for an insanity plea, and most states will simply throw the perpetrator in jail like any other criminal if that is their mental illness, since though such persons may have the adequate Lack of Empathy that you can say they don't appreciate the moral reasons for why their crimes were wrong, in general they still understood that they were breaking the law, and having pathalogical justifications for doing so isn't good enough. However, other countries such as the United Kingdom do accept these as valid grounds, and many notorious British Serial Killers are locked up in mental institutions whereas in America they would be in jail, probably waiting for the Death Penalty. Such British prisoners, however, are usually not expected to ever be released and most of their appeals fail. In fiction, many cases of the Insanity Defence are often based on personality disorders, even if they are American.

Anime and Manga

 * In Tokyo Babylon, Subaru encounters a woman who is trying to summon a dog spirit to kill the man who murdered her young daughter, since he had been deemed too insane to stand trial. She plans on using the insanity defense for herself afterwards, figuring that a judge would see the "attempted" ritual as proof that she had lost her mind before killing the man herself.

Comic Books

 * In The DCU, most of the inhabitants of Arkham Asylum for the Criminally Insane have had a successful Insanity Defense entered on their behalf. Many of them are also, not coincidentally, crazy. However most of them are not legally insane by any reasonable interpretation. A pathological obsession with hats, cats, birds, or riddles does not mean someone isn't aware of what they're doing. The same goes for being an eco-terrorist, wanting to eat people, or most of the various eccentricities Batvillains develop while pursuing a criminal career.
 * During the Golden Age and The Interregnum, the Joker was not considered insane enough to qualify for this defense. When he tried it, Batman easily proved that despite Joker's eccentricity, he was fully capable of understanding the illegality and consequences of his actions. It was only when the Joker became a homicidal maniac in the 1970s that Arkham Asylum became a necessity for him.
 * In The Joker: Devil's Advocate, a new D.A. decides to go for broke and push for the death penalty after a series of killings with the Joker's MO. After a "Trial of the Century" with accompanying media circus, he is found guilty and sentenced to death. However, he claims to have no knowledge of the murders. Batman, who has never known the Joker to deny any of his crimes, investigates and finds out that this time he really is innocent. Joker is returned to Arkham when this is revealed..
 * The nearly abusive use of this defense among Batman villains in particular has caused more than one rant from real legal professionals. It concluded that only Two-Face and sometimes The Joker are "legally" insane, though it's an old and incomplete list.
 * The general consensus is that the insanity defense is almost guaranteed to work in the Gotham court system regardless of how much sense it makes legally but since it means going to Arkham, you'd need to be crazy to try it. In Arkham Asylum Living Hell, one white-collar criminal, unfamiliar with Gotham, made this mistake and found himself in Arkham instead of the cushy rehab center he expected to be sent to. Things didn't go well for him.
 * Also, not everyone who gets sent to Arkham is sent there due to being considered insane. Mr. Freeze is (usually) sane, but he's still there because it's the only imprisonment facility with the technology to keep a cell refrigerated enough for him to survive in it. Granted, this probably counts as an abuse of his human rights because it keeps him from interacting with sane people, but he hates everyone anyway so he won't complain.
 * When Hal Jorden, Green Lantern, fought an opponent codenamed the Aerialist, it became obvious that the Aerialist was under a severe delusion making him believe his criminal actions were entirely legal and correct. Hal referenced the M'Naghten rules when wrapping up the case, his opinion being that the Aerialist would qualify for an Insanity Defense.

Film
"Rico: I remember you. Testified before the Council that I was insane, right?
 * In Anatomy of a Murder, the defense's entire argument rests entirely on the "irresistible impulse" insanity defense.
 * In Arsenic and Old Lace, the hero Mortimer attempts to get his sweet old aunts committed to a psychiatric institution after learning of the multiple murders they've committed and hidden in their basement. The hilarity comes from the fact that nobody will believe that they are insane unless he reveals why he wants them committed, so he has to trick them into going.
 * In Batman Begins, Dr. Johnathan Crane (aka The Scarecrow) helps mob boss Carmine Falcone by testifying to the insanity of Falcone's thugs and having them put in Arkham Asylum to avoid jail time. But while there, he does twisted experiments on them to drive them to insanity.
 * Aversion in Nuts, where Barbra Streisand demands they declare her sane. The film notes (accurately) that if you are declared insane, you can be kept locked up for life, even for a crime that would only entail a few years in prison.
 * Primal Fear, A Time To Kill and One Flew Over the Cuckoo's Nest, each a Film of the Book.
 * One Flew Over the Cuckoo's Nest is actually a bit of a subversion of it; playing insane got McMurphy transferred into a mental institution, which he knows about and thinks that's better than prison. He is sorely mistaken.
 * Training Day: Mentioned by one of the three wise men when he recaps to Alonzo how an off-screen criminal recently got off this way by pulling a stunt in court that made him seem mentally unsound.
 * Judge Dredd (movie only)

Ilsa: And therefore innocent. I was trying to save your life.

Rico: What you did was insult me, 'cause I knew exactly what I was doing. Then and now."


 * M is basically a gigantic and brilliantly subtle Author Tract in defense of this. Hitler hated that movie, once someone explained it to him.
 * Depending on which version you watch, William Friedkin's Rampage is either the opposite, or agrees.
 * Inception inverts this; had herself declared sane by three different psychiatrists, so as to prevent  from being able to explain the nature of her madness, as part of her plan.

Literature
""...The landlord shouted to them to leave him alone, for he had already told them that he was mad, and as a madman he would not be accountable even if he killed them all...""
 * Primal Fear. After the trial starts, an accused murderer's attorney realizes that his client has Multiple Personality Disorder (i.e. split personality) and that one of the personalities committed the crime. He tries to change his plea from "Not Guilty" to an Insanity Defense. After a dramatic courtroom scene the judge agrees and sentences the client to a mental hospital for treatment. . The concept remains in The Film of the Book.
 * The killer, for all his cunning, seems not to be aware of the "institutionalization is usually longer than prison" trope.
 * On the other hand, in the sequels he manages to fool his doctors into thinking he's cured and get out-where he kills again.
 * In A Time To Kill the defence lawyer protagonist argued that the rape of his client's daughter combined with the likelihood of them getting off lightly drove the defendant temporarily insane, causing him to kill both rapists with an assault rifle. This plea is somewhat undermined when the prosecution points out that the psychiatrist he brings in to support his argument was convicted of statutory rape and pressures the defendant into angrily declaring that he still thinks the rapists deserved to die, but in the end he's found not guilty (although the jury's exact reasoning is not revealed).
 * Actually, the reasoning IS explained. One of the jurors performed the thought experiment used as a closing argument in the film. The jury realized just how much the rape had to shatter Carl Lee and voted to acquit. Notably, this is one case where the actual results of on insanity plea would likely match the fictional. As it was a temporary phenomenon brought on by a unique strain, he would probably not be required to attend treatment.
 * A jury may very well be inclined to vote against conviction in a case where an otherwise law-abiding citizen shot the men who brutally raped and tried to murder his daughter. But the laws in the American justice system that protect killers who were temporarily incompetent are not intended to apply in scenarios like the one involving Carl Lee. (Certainly, if Lee had been at a shooting range with a gun in his hand when he learned that the man standing next to him had raped his daughter and tried to kill her, he would be an ideal candidate for such a defense, because of the lack of premeditation combined with the shock he would have experienced.) But the circumstances involved Lee obtaining a gun, bringing it to court, and waiting until he was in close proximity to his daughter's rapists, and then shooting them. With that level of premeditation, a man like Carl, who did not suffer from any mental disorders, is supposed to be excluded from the protection of those laws. Some people, this troper included, would like to see the protections of those laws expanded, but until that day comes, a jury that voted against conviction would be disregarding the law, and substituting their own sense of right-and-wrong.
 * Which is perfectly legal in the US. Jury Nullification is a constitutional right for a jury to find a defendant not guilty, even if the evidence shows him/her to be guilty of the crime, if the jury feels the defendant doesn't deserve punishment.
 * Historically, juries judged both the law and the facts, according to their sense of justice, as the "conscience of the community." Judges do not permit defense attorneys outright arguing for jury nullification though, so the thought experiment in the story might not be allowed in Real Life. In any case, once the jury has rendered a verdict of Not Guilty, it's final, no matter what the reasoning, whether explained or not. We can find many examples for this.
 * One Flew Over the Cuckoo's Nest - McMurphy CLAIMS to haven gotten himself transferred to the institute to serve out the rest of his sentence in cushy surroundings, and is more than a little alarmed when he realizes that 'the rest of his sentence' is no longer the few months he thought it was, but when the doctors decide that he's no longer a threat to himself or others -- which, considering he's pissed off the evil Nurse Ratchet, could mean an indefinite stay. It Got Worse, of course.
 * Comes up in The Krytos Trap. Tycho Celchu is accused of murder, and there's a lot of evidence that he did it. A few years ago, he'd been kidnapped by Ysanne Isard, Manchurian Agent maker extraordinaire. People who think he did it are divided between thinking that he'd been brainwashed and thinking that he was a garden-variety traitor; there's evidence for both. His lawyer tells Tycho that if the Tribunal decides he was brainwashed, he'll be declared not guilty by reason of diminished sapience and put into a hospital to be treated, released when he's cured. That sounds nightmarish to Tycho, but the Tribunal's nightmare is that he'll only be there for a week or two before treatment ends and he'll be released. This would make the justice system seem impotent; the nonhuman public thinks he's a traitor and isn't very sure about their government as is. The human public is starting to believe that he's actually innocent, since there's proof of that too, and is being offered up to placate the nonhumans. It's sticky.
 * In Red Dragon and Silence of the Lambs, Dr. Hannibal Lecter was committed to a mental hospital after being convicted of killing and cannibalizing several people and the attempted murder of an FBI agent. The hospital's director Dr. Chilton describes him as a "pure psychopath". Lecter's case wouldn't fit the legal definition of insanity since, based on the discussions he had with Starling and others, it's clear that he was in full possession of his (admittedly impressive) mental faculties and capable of understanding the consequences of what he was doing. In Hannibal Starling explains that Lecter did not actually plead insanity, but rather that it was the jury that found him insane, the reasoning of the courts being that Lecter was such a respectable, successful, and intelligent individual that the only possible explanation for his crimes was that he was stark raving mad.
 * In the Film of the Book the headlines read "Lecter Given Nine Life Sentences" or something like that, but he is still put in a mental institution for treatment, which does occur even when the defendant is found guilty but still has a disorder.
 * Older Than Steam: In Don Quixote, Cervantes explains this trope is the reason why Don Quixote is never killed or sent to jail (though he is often beaten) by the poor Innocent Bystander of the day. Note that it's another character who invokes it, because Don Quixote himself cannot, since he obviously is not mad -- those jealous wizards transmuted the giants into windmills! It may be the Ur Example.


 * Parodied in Soul Music, when a murderer who has already been executed tries to convince Death that "the balance of my mind was disturbed". His logic? "I really wanted to kill him. You can't tell me that's a balanced state of mind."

Live Action TV

 * The Made for TV Movie The Burning Bed is a good example of a well-supported "temporary insanity" plea.
 * Law and Order frequently addresses this, as many defendants plead 'not guilty by reason of mental disease or defect' (which is how they phrase it) and court / prosecutorial appointed psychiatrists are often featured for this reason; rarely are the defendants actually found to be legally incompetent to the degree that is required by law for such a plea to be accepted without trial, and even fewer actually have this plea accepted by a jury. The Catch-22 bind is often addressed in episodes where the situation is inverted; the defendant clearly is mentally incompetent, but insists they are sane.
 * One episode has the unusual spectacle of a guy using an insanity defence while defending himself. His claim is that he was insane when he committed the crimes, but now is normal thanks to medication, so it's not as ludicrous as it first seems. He is a paranoid schizophrenic, leading to him becoming homeless and murdering people due to his delusions. Before, however, he earned a law degree, and is practicing (defending himself) the first time.
 * One inversion occurred when an obviously insane defendant who murdered three people refused to allow his attorney to plead insanity... even though he was obviously guilty... and he was eligible for the death penalty if convicted.
 * On Law and Order Special Victims Unit, sexsomnia, watching too much TV (Oz), borderline mental retardation (as noted below), schizophrenia, sexual addiction, even a brain tumor have all been successfully proffered as rape defenses, and in nearly all of these cases, the defense is valid. As with the mothership, defense lawyers still habitually trot out the defense as a last resort when the client is caught red-handed only to get their asses handed to them when a last-minute fact torpedoes their whole case.
 * It's used to chilling effect in an episode where a mentally disabled man rapes an old woman (causing her to have a heart attack) because her position greatly resembles a porn flick he was shown, and he didn't understand the nature or consequences of what he was doing, thus acquitted. The prosecutor is infuriated that he 'got off easy' by not being put in prison--but then it cuts to the man being put by one of the detectives into a mental institution, still unsure of what's going on, and seeing the various mentally disturbed people talking to themselves or wandering around in an unpleasantly gray facility. The final shot is the horror on the man's face.
 * Subverted in episodes of both shows when insane defendants refused to plead insanity for different reasons, forcing the prosecutors to come up with a roundabout way to introduce the evidence of their insanity or compel them to reveal it by goading them into a courtroom outburst of some sort.
 * In one episode of Law and Order: Criminal Intent, the user of the insanity defense is a police psychologist.
 * Parodied in Community. The Insanity Defense is used by Jeff to keep Britta from being expelled from Greendale, arguing that she deliberately sabotaged herself by cheating on a test in order to fail and get kicked out, thus validating her own low sense of self-worth. He then goes on to argue that since everyone at Greendale is crazy in one sense or another, it would be an act of gross hypocrisy to kick her out based on this. It actually works.
 * Used in Bones.  was deemed insane in an off-screen trial, and went to a mental institution. Eventually, the audience finds out that
 * One episode of Criminal Minds has Hotch tell the killer himself "you were sick. You didn't know what you were doing", because the man is freaking out while in custody, having just realized that he is actually guilty of the crimes they're accusing him of. The last shot of the episode is the killer in a mental institution. There are a number of other episodes where you don't see the killer in an institution, but it's pretty obvious that the defence applies.
 * The Firm on The Practice would cut-and-paste the Insanity Defense around any sympathetic defendant who performed a Vigilante Execution to give the jury an excuse to acquit their client since arguing an eye for an eye would be considered jury nullification. The chances of a jury buying it were generally low.
 * The episode "Committed" showed the aftermath of one these: a serial killer who used a successful insanity defence some years ago hires Lindsey to help him get declared sane and released from the institution he is now in.
 * Attempted by Serial Killer Nate Haskell in CSI, who argues that a combination of childhood abuse and possessing the MAOA gene, which has been linked to an increased propensity for violence, turned him into a sadistic psychopath. His Arch Enemy Ray Langston shoots him down in court by announcing that he also had an abusive childhood and also possesses the gene, but he became a doctor rather than a murderer, and Haskell later admits in private that he made a conscious decision in his youth to blame everything on the two in the event he was caught.
 * This would be a Crowning Moment of Awesome for Langston, were it not for the sheer amount of Fridge Logic involved in the case- it is strongly implied that if Haskell were found insane, he would actually be let out of custody, despite his entire defence boiling down to "I'm a sadistic, murdering psychopath. And I'll probably do it again."

Radio Drama

 * "Tabard of Pizarro", an episode of Bold Venture, had the guest star claim that he was framed for murdering his wife, and pled insanity so as to be free to eventually claim his revenge. (The villain of the story tries to frame the protagonist for murder during the course of the episode, so it seems likely the guest star is telling the truth.) Unfortunately, it was many years before he was considered fit to be released.

Web Comics

 * Saturday Morning Breakfast Cereal has a man defending his insanity plea with "Well, I killed a whole bunch of people. Crazy enough for ya?" Refuge in Audacity, but as explained above, not quite good enough.
 * Also inverted here

Western Animation

 * In the Futurama episode "Insane in the Mainframe", Simple Country Lawyer Hyperchicken uses the insanity defense in favor of Fry and Bender, and offers as proof the fact that "they done hired me as their lawyer." What then happens is that they're put in the mental institution, similar to what would have happened real life if they weren't found "Guilty but Mentally Ill".
 * Note that this in a country where being poor has recently been classified as a mental illness.
 * Judy suggests using this excuse when Doug is framed for stealing Mr. Bone's trophy. Doug mentions that someone else actually tried that before but still got in trouble and had to go to the school counselor twice a week.
 * In an episode of Batman: The Animated Series, a sane crook decides to plead insanity, and won his case. He then gets sent to Arkham Asylum. Insanity ensues.
 * Subverted in an episode of Harvey Birdman, Attorney at Law. Harvey tries to use this defense to acquit his client, and it looked like the jury was going to buy it...and then a talking tapir points out that the defense can only be used in criminal cases. Harvey was defending a man in a lawsuit.

Video Games

 * The first Phoenix Wright: Ace Attorney game had an Amoral Attorney pressure his client into using an insanity defense..
 * In Knights of the Old Republic, if you let the lawyer appointed to you handle the trial (without telling him that you have evidence of a Sith plot) after then he'll try this as a last defense. It fails, and you're executed in a Nonstandard Game Over.
 * In Remember 11, Keiko Inubushi avoided going to prison after murdering twelve people due to suffering from Dissociative Identity Disorder. Instead, she was sent to the SPHIA psychiatric hospital.
 * In Corpse Party, this is how Yoshikazu Yanagihori avoided going to jail for abducting four children and killing three of him. He actually was pretty insane at that point, so a mental hospital was probably the best place for him. Unfortunately, security was not very good (it was 1973 Japan) and he ended up breaking out. He then broke into the school where the children were killed and hanged himself.

Real Life

 * Louis Riel's lawyers wanted him to plead insanity to be found not guilty of treason. We'll never know if it would have worked, because Riel wanted to use his time in court as a final opportunity to make public the natives' problems.
 * One notable case in British legal history (it led to the end the rule of "constructive malice", aka Felony Murder) was the case of Derek Bentley and Christopher Craig in 1952. Bentley, 19, was severely mentally disabled, although not insane. Craig was 16. When breaking into a warehouse one night, Craig was carrying a gun. Confronted by the police, Bentley (just arrested by one of them) allegedly said "Let him have it, Chris!". Craig shot dead another police officer. Craig was too young to be hanged (it was for 18-year olds and above only) and received "detention at Her Majesty's pleasure", paroled after 10 years. Bentley was hanged. In 1993, he was retroactively pardoned and his sentence quashed in 1998.
 * Sweden recently had a case where the psychiatrists employed by the court found the (convicted) criminal insane. He was sent to an institution - and discharged the next day, because the doctor in charge of the institution didn't agree with the assessment.
 * One of the better known cases in recent American history was the murder of Supervisor Harvey Milk and Mayor George Moscone in San Francisco. Former Supervisor Dan White's defense team was able to convince the jury that he was in such a mental state as to be incapable of premeditation, so he ended up being convicted of voluntary manslaughter. Among other things, they cited White's shift from health nut to junk food addict as evidence of his declining mental state. The references to junk food led to the coining of the term "Twinkie Defense".
 * Although the term "Twinkie Defense" is often used nowadays to mean that eating the twinkies caused him to enter the state of diminished capacity. This argument was not actually used by the defense, but people think it was.
 * A man in Alberta beheaded a fellow passenger on a Greyhound bus. He was found not criminally responsible because he is insane. He was, however, deemed a significant risk--which means he will likely spend the rest of his life in a rubber room.
 * A lot of people misunderstood what the verdict meant for the defendant, and there was some anger that he wasn't found guilty. Others, of course, pointed out that while he might not be in an actual prison, he'd spend a lot longer in a psychiatric institution--essentially, instead of "life with chance of parole in some number of years", he got "life with no real chance of parole".
 * A man strangled his wife in his sleep and was released as it was decided that his sleep disorder meant that he wasn't responsible for this act. New Scientist has included a disussion of how you can show whether or not someone has a sleep disorder (after staying awake for 25h a given tone woke up all the sleep disordered positive controls and non of the healthy controls).
 * John Hinckley, Jr attempted to assassinate Ronald Reagan and is one of the few "successful" Insanity Defense stories. The verdict led to widespread dismay; as a result, the U.S. Congress and a number of states rewrote laws regarding the insanity defense. Idaho, Montana, and Utah have abolished the defense altogether. The dismay is ironic, as he has spent almost 30 years in a mental institution, probably more time than he would have spent in prison if convicted, certainly longer than many "sane" murderers spend in prison.
 * The US Supreme Court ruled that people who are insane can not be executed. However, if medication can make someone sane, they can be forced to take it so they can be executed.
 * That sounds patently absurd, if the crime was committed during insanity without the aid of medication.
 * If that was the case then they probably would be sent to an institution and thus never be even considered for execution.
 * The ruling refers to once-sane defendants on Death Row who gradually go mad from spending years on Death Row. The court ruled that in such a case, the state can force the defendant to be medicated to render them sane for their execution.
 * The lawyers of Serial Killer Herbert Mullin tried this. Somewhat bizarrely, it didn't work, as it was considered that his crimes were too well-planned to be the work of an insane person, even though his motive was that he had a delusion that he had to kill people lest a whole coast of the US be wiped out by natural disasters.
 * The Richard Chase trial was similar.
 * Jared Loughner is an interesting example of just how hard it is to pull this off in real life. Prior to killing six people, he'd been forced out of college and told he couldn't come back unless he could maintain a mental health clearance proving he wasn't a danger to himself and others. The sheer incoherence of his political and philosophical ramblings got him ejected from abovetopsecret.com, one of the more out-there conspiracy theory sites on the Internet, and countless witnesses on and off-line report him as having done everything from accusing his math teacher of "denying math" to spending thirty minutes in a bathroom and asking afterwards what year it was. As of this writing, it's thought that he'll probably be declared sane.
 * This is largely because, unlike laymen, psychiatrists, doctors, and most importantly lawmakers, do not measure insanity by quirkiness or social ineptitude. In fact, insane people are often very socially adept (especially psychopaths with ulterior motives). Plus, while their insanity, by definition, makes them quirky in some sense, they often hide it well. For instance, insane people sometimes eat feces, but the ones who do will rarely, if ever, do so in public (though it does happen). Also their quirkiness is a symptom of their insanity, not the insanity itself. He's certainly proven to be weird, but that is not the same as being proven insane under law.