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What Is the Insanity Defense?

Posted on February 22, 2021 in Criminal Defense

Insanity is a controversial and uncommon defense strategy used in criminal law. This defense asserts that the accused party – the defendant – was legally insane at the time he or she committed a crime and therefore should be found not guilty.

Studies show that only about 1% of all felony cases in the US use the insanity defense. Furthermore, it only succeeds about 25% of the time. When successful, however, the insanity defense can lead to a not-guilty verdict for the defendant.

What Does it Mean to Plead Insanity?

Using insanity as a defense during a criminal case asserts that the defendant was legally insane at the time the crime was committed and was therefore incapable of determining right from wrong or understanding the consequences of his or her actions. Since almost every crime in the US justice system requires intent to commit the crime for a conviction, the insanity defense can successfully prevent a conviction by proving the defendant could not have intended to commit the crime due to his or her mental disease or condition.

What Must One Prove to Use the Insanity Defense?

Prior to 1982, the burden of proof when using the insanity defense rested with the prosecutor. It was the prosecutor’s responsibility to prove beyond a reasonable doubt that the defendant was not insane. The acquittal of John W. Hinckley for the case against him for the attempted assassination of President Ronald Reagan, however, changed this law. After his acquittal, many states reversed their insanity laws to require the defendant to fulfill the burden of proof instead.

Today, the burden of proof when using the insanity defense rests with the defendant. It is the defense’s responsibility to prove that the defendant was legally insane at the time of committing the crime. This burden is not proof beyond a reasonable doubt, however; it is a preponderance of the evidence, meaning clear and convincing evidence that the defendant was insane.

Four Tests for Establishing Insanity

Within the criminal justice system, there are currently four different tests that may be used to establish a defendant as legally insane. The test or combination of tests that must be used depends on the laws in the state where the trial is taking place:

  1. The M’Naghten Rule test. This is the most commonly used rule around the world today. It asserts that the defendant was unable to distinguish right from wrong due to a disease of the mind that renders the defendant incapable of understanding his or her own actions.
  2. The irresistible impulse test. With this test, a defendant is legally insane if he or she has a mental disorder that makes it impossible for the defendant to resist committing an act known to be wrong or illegal.
  3. The Model Penal Code test. This test holds that the defendant has a diagnosed mental disorder that prevents him or her from acting within the confines of the law or understanding the criminal nature of his or her actions.
  4. The Durham Rule test. Used only in New Hampshire, this test holds that if the defendant only committed the crime because of his or her mental disease or defect, the defendant will be found not guilty by reason of insanity.

In certain states, using the insanity defense is not a possibility. The laws in Montana, Idaho, Kansas and Utah do not explicitly allow a defendant to use the insanity defense to argue for a not-guilty verdict. Rather than allowing the insanity defense to result in a not-guilty verdict, these states permit defendants to be found “guilty, but insane.” This type of verdict will result in the defendant being institutionalized for his or her mental health rather than going to prison.

Learn more about the insanity defense by contacting a Phoenix defense lawyer.