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What Is the Insanity Defense?

Understanding Criminal Insanity & Its Role in Your Defense

You may have heard cases in which a defendant pleads “not guilty by reason of insanity.” The insanity defense is a controversial matter because it justifies the reasoning behind the commission of an alleged crime by deeming a defendant “insane.”


But what does “insanity” mean in the context of criminal cases?

In sum, declaring a defendant “criminally insane” means they have a mental defect or disease that prohibits them from understanding their wrongful actions. Under federal law, the burden of proof requires the defendant to prove “ … their insanity by a standard as high as beyond reasonable doubt … [by providing] clear and convincing evidence …” Psychiatric testimony, the defendant’s medical and criminal history, and other evidence may help support the insanity defense.


FL Insanity Law

Under Florida’s insanity defense law, “All persons are presumed to be sane. It is an affirmative defense to a criminal prosecution that, at the time of the commission of the acts constituting the offense, the defendant was insane. Insanity is established when: The defendant had a mental infirmity, disease, or defect; and because of this condition, the defendant  did not know what he or she was doing or its consequences; or although the defendant knew what he or she was doing and its consequences, the defendant did not know that what he or she was doing was wrong.”


Types of Insanity Defenses:

To prove criminal insanity, a host of tests are used to determine whether a defendant’s mental disease or incapacity resulted in the commission of a crime. They include:

  • M’Naghten insanity defense: This is a criminal insanity test used to determine if a defendant’s mental incapacity prohibited them from understanding the nature of their actions and/or the fact that their actions were wrong.
  • Irresistible impulse defense: If a defendant could not resist the impulse to commit the crime in question due to their mental illness, even if they knew their actions were wrong.
  • Substantial capacity test: Under this test, “A person is not responsible for criminal conduct if at the time of such conduct as a result of mental disease or defect, he lacks substantial capacity either to appreciate the criminality [wrongfulness] of his conduct or to conform his conduct to the requirements of law.”
  • A.L.I standard: This introduced the use of medical and psychiatric evidence when proving criminal insanity. The American Language Institute (ALI) standards hold that a defendant will not be held criminally responsible for their alleged crime if, “As a result of a mental disease or defect [they lack] substantial capacity either to appreciate the criminality of their conduct or to conform [their] conduct to the requirements of the law.”

The insanity defense is viable if a defendant can “pass” these tests. As seasoned criminal defense lawyers with 25 combined years of experience, we understand when and how to employ this strategic defense successfully and will determine if the insanity defense supports your case once you retain our representation.

We encourage you to contact us to discuss your case and learn how we can best serve you.

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