Criminal Insanity: Cases, Law & Defense

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  • 0:03 What Is Criminal Insanity?
  • 1:09 Landmark Cases
  • 3:10 Law & Defense
  • 4:41 Lesson Summary
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Lesson Transcript
Instructor: Brittany McKenna

Brittany is a licensed attorney who specializes in criminal law, legal writing, and appellate practice and procedure.

Criminal insanity is a legal defense that may be used to avoid criminal responsibility. This lesson will introduce you to the concept of criminal insanity and provide examples of notable cases involving the defense, as well as the tests used to determine if a defendant is criminally insane.

What Is Criminal Insanity?

It's often said that the definition of insanity is doing the same thing over and over and expecting a different result. But in the context of criminal law, insanity means something entirely different. For example, insanity may exhibited by someone stabbing another person during a sleepwalking episode or trying to assassinate the president to impress a famous actress.

Criminal insanity is a legal defense used by a criminal defendant to avoid being convicted of a crime. Under this defense, the defendant must prove that he or she suffered from a mental health episode at the time the crime was committed. A mental health episode may include a mental illness, defect, or disease.

In every criminal trial, the prosecution has to convince the jury that the defendant possessed a guilty state of mind when he or she committed the crime. The insanity defense allows a defendant to prove that he or she lacked the requisite mental state to be found guilty of a crime. Without proof of a guilty state of mind, the prosecution can't prove its case.

Landmark Cases

A pair of British cases from the 1800s are often used to illustrate the insanity defense.

In 1800, James Hadfield entered the Theatre Royal in London's West End and fired a pistol at King George III as he stood in the royal box. Although Hadfield's assassination attempt was unsuccessful, he was immediately apprehended and charged with treason. At Hadfield's trial, his defense attorney argued that Hadfield was insane at the time of the shooting. Medical experts testified that they believed that head injuries suffered in battle rendered Hadfield incapable of understanding the criminal consequences of his actions. Hadfield was acquitted and later committed to an insane asylum.

In 1843, a Scottish woodworker named Daniel M'Naghten approached civil servant Edward Drummond on a busy London street. Without provocation, M'Naghten drew his pistol and shot Drummond in the back. M'Naghten, who believed that he was being followed by political spies, mistook Drummond for the prime minister. Drummond died five days later from his injuries. M'Naghten was arrested and tried. At his trial, M'Naghten's defense attorneys argued that he suffered from delusions so powerful that he lacked control over his actions. After multiple medical experts testified in support of the theory of insanity, M'Naghten was acquitted. Like James Hadfield, M'Naghten lived out his days in an asylum.

One of the most famous examples of the insanity defense was featured in the trial of John Hinckley, Jr. In the early 1980s, Hinckley became infatuated with the actress Jodie Foster after watching the film Taxi Driver. As his obsession grew, Hinckley began to stalk Foster and made various attempts to contact her. In 1981, Hinckley tried to shoot President Ronald Reagan as he left a hotel in an attempt to get Foster's attention once and for all. In his subsequent trial, Hinckley was found not guilty by reason of insanity.

Law & Defense

Over the years, courts and legal scholars have created different legal tests defining what it means to be criminally insane.

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