Why do we allow a guilty defendant to be found not guilty by reason of insanity?
The insanity defense is based on the principle that punishment for serious crime is justified only if defendants were capable of controlling their moral behavior and could appreciate the wrongfulness of their behavior at the time the crime was committed. Insane people (people suffering from a mental disease) are not moral actors, the reasoning goes, and so should not be criminally punished for acts committed because of the insanity.
The Insanity Defense Remains Controversial
Though the insanity defense was recognized in England as early as 1505, it remains controversial. Many people point out that a person killed by an insane person is just as dead as one killed by someone who is sane, and argue that people should be punished for the harms they cause regardless of their mental functioning. Opponents of the insanity defense also doubt the competence of psychiatrists, judges, and jurors to determine after the fact whether someone suffered from a mental disease at the time the crime was committed, and the connection, if any, between mental disease and the commission of crime. Perhaps due to popular dissatisfaction with the insanity defense, few defendants actually rely on it. And of the defendants who do, very few are actually found not guilty by reason of insanity.
What is the most widely used definition of insanity?
The most popular definition is the "M'Naghten rule," established in England in the 1840s. Under the M'Naghten rule, defendants are not guilty by reason of insanity if at the time of a crime they were afflicted with a mental disease which caused them to not know what they were physically doing (lack of cognitive capacity), or if they did know, that what they were doing was wrong (lack of moral capacity).
States have the power to adopt their own insanity definitions. Arizona, for example, recognizes only the "lack of moral capacity" aspect of M'Naghten. In other words, defendants are sane under Arizona law if they understand that their actions are wrong.
Do courts use other definitions of insanity (besides the M'Naghten rule)?
Yes. Courts within the same state may use different definitions of insanity. A defendant who is not insane under one definition may be insane under another. For example, another common definition of insanity accepted in some states is known as "irresistible impulse." (This defense was the focus of the famous courtroom movie Anatomy of a Murder.) Defendants who acted because of an irresistible impulse knew that their actions were wrong, and thus would be considered sane under the M'Naghten rule. However, they may still be considered insane under the irresistible impulse rule if at the time of the crime they were afflicted with a mental disease that rendered them unable to control actions that they knew were wrong.
If I'm found not guilty by reason of insanity, will I be set free?
Probably not. Defendants found not guilty by reason of insanity usually are confined to mental institutions, and not released until a court determines that whatever insanity they experienced at the time of the crime is no longer present. Because judges do not want repeat performances from insane defendants, a defendant found not guilty by reason of insanity can easily spend more time in a mental institution than the defendant would spend in prison had the defendant been convicted of the crime.
Can defendants be found both guilty and insane?
Yes. Many states follow a "guilt first" procedure. In these states, a defendant's sanity is not determined until after a defendant has been found guilty of a crime. Then, if a defendant is found to have been insane when a crime was committed, the defendant is placed in a mental hospital. When (and if) the defendant's sanity is restored, the defendant goes to prison to serve any remaining time on the sentence.
Do I need a psychiatrist to testify that I was insane?
In almost all cases involving insanity, yes. When a defendant enters a plea of not guilty by reason of insanity, a psychiatric expert examines the defendant on behalf of the defense. The psychiatrist's investigation will normally include the circumstances of the crime, the defendant's past history, and one or more personal interviews of the defendant. It is not unusual in this kind of case to see two experts emphatically disagree on just about everything (which causes some to question whether psychiatry is an exact enough science to be used as expert testimony in the first place).
Friends and Relatives as Defense Witnesses
The strongest evidence of insanity is often provided by friends and relatives who have known the defendant long enough to form a reliable opinion that the defendant is mentally ill. Most jurisdictions allow nonexpert witnesses to give an opinion regarding the sanity of a person with whom the witness is well acquainted.
Competence to Stand Trial
Whether or not a defendant pleads insanity as a defense to criminal charges, an issue can arise as to a defendant's sanity at the time of trial. A defendant cannot be put on trial if she suffers from a mental disease that prevents her from understanding the proceedings and assisting in the preparation of the defense. If a defendant claims incompetence to stand trial, a judge will hold a hearing and take evidence concerning the defendant's current competence. At this hearing, the defendant has the burden of proving incompetence to stand trial by a preponderance of the evidence. (Cooper v. Oklahoma, U.S. Sup. Ct. 1996). If the judge decides that the defendant is mentally incompetent, the defendant will probably be placed in a mental institution until competency is reestablished. In what the U.S. Supreme Court has said are likely to be "rare" circumstances, prison officials can legally force prisoners to take medications that would make them competent to stand trial (Sell v. United States, U.S. Sup. Ct. 2003). Once a prisoner regains competence, with or without the help of medication, the trial will take place.