Not Guilty by Reason of Insanity

Many television and movie defendants are found not guilty by reason of insanity. However, real criminal defendants are not as successful with the insanity defense as popular media seems to suggest. One study found that the insanity defense is only used in about 1% of all court cases and is only successful in about 26% of those cases. So, only approximately one quarter of one percent of cases in the U.S. judicial system end with a defendant being found not guilty by reason of insanity.

What is the Insanity Defense?

The insanity defense is a possible defense to a criminal matter. In order to assert the defense of insanity, a criminal defendant must claim that he should not be criminally liable for breaking the law because he was insane when the alleged crime occurred.
The definition of insanity varies among different jurisdictions. However, it is important to note that for purposes of a legal defense, the term insanity is governed by a jurisdiction’s statutory and case law and not the medical definition of mental illness. 
Most jurisdictions require a professional to find that the defendant was not capable of distinguishing between right and wrong at the time of the offense. Some jurisdictions have an additional element where a defendant can be found not guilty by reason of insanity if he was not able to control his behavior at the time of the offense. Still other jurisdictions have abolished the insanity defense, a move that the Supreme Court has upheld.

How Can a Defendant be Successful in His Insanity Defense?

Usually, a defendant will need to have a complete mental evaluation as a first step in his insanity defense. Psychiatrists or psychologists will likely take the stand and testify about the defendant’s likely state of mind at the time of the offense. However, even these professionals cannot decide whether or not a defendant is insane because, as discussed above, insanity is a legal term when used as a criminal defense. Therefore, the jury or judge will decide whether the testimony and evidence support a finding of criminal insanity.

What Happens if the Court Finds a Defendant Criminally Insane?

Often, the defendant will be committed to a psychiatric hospital if he was found to be responsible for the alleged crimes but not guilty by reason of insanity. Typically, the commitment is not for a set amount of time but rather until the individual is deemed not to be a threat to society.

Temporary Insanity

A defense of temporary insanity is also difficult to prove. If a defendant asserts temporary insanity as a defense then he is asserting that he was insane at the time of the alleged crime but is sane now. If a court accepts this defense, then the defendant usually is not committed to a psychiatric facility and is found not guilty of the offense.
While the successful use of the insanity defense may be rare, its existence imposes an important moral check on the legal system. Specifically, it allows the law to impose treatment rather than punishment on people who lack the capacity to understand their actions. It therefore, protects society, while seeking to provide help and possibly rehabilitation to the offender.

The information on this page is meant to provide a general overview of the law. The laws in your state and/or city may deviate significantly from those described here. If you have specific questions related to your situation you should speak with a local attorney.

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