The 'Model Penal Code' Test for Legal Insanity

The MPC rule combines these elements. The MPC test asks whether the defendant could fully understand the criminality of their conduct or whether they could conform their behavior to the law. The MPC rule also requires that a licensed mental health professional diagnose the mental disease or defect.

In criminal law, prosecutors generally must show that a defendant willfully intended to commit a crime to secure a conviction. If the trier of fact finds a criminal defendant legally insane, there can be no willful intent. A defendant not guilty by reason of insanity is not liable for crimes resulting from their mental illness.

A defendant facing criminal charges may assert an insanity defense in various circumstances. State courts use insanity tests to determine whether someone was insane at the time of the crime. These tests include the following:

This article focuses on the Model Penal Code test, the modern standard used to determine legal insanity.

Model Penal Code Test for Legal Insanity: History

Courts widely adopted the Model Penal Code test from the American Law Institute (MPC test) in the 1970s. But it fell out of favor when a jury found John Hinckley, Jr. not guilty by reason of insanity for his attempted assassination of President Ronald Reagan in 1981.

Hinckley had a troubled background, but he did not exhibit overt signs of mental illness. But at his trial, his obsession with the movie “Taxi Driver" and one of its stars, Jodie Foster, was on full display. In the film, the lead character, Travis Bickle, is a lonely and depressed taxi driver who plots a political assassination and the rescue of a young prostitute. Evidence presented at trial indicated Hinckley identified with Bickle and tried to emulate him. Hinckley tried to assassinate President Reagan to impress Jodie Foster.

The jury found Hinckley not guilty by reason of insanity. The nation exploded with outrage over the acquittal. Within a month after the verdict, Congress held hearings about the insanity defense. Congress followed up with legislation to shift the burden of proof regarding insanity from the prosecution to the defense. It also narrowed the definition of “insane."

State jurisdictions followed suit. State law changed to be in line with the Congressional findings. Today, most states place the burden on the defense to prove insanity. Some states have a finding of “guilty but mentally ill." Other states, like Montana, Idaho, and Utah, abolished the defense of insanity altogether.

Model Penal Code Test for Legal Insanity: Basics

Under the MPC test, a criminal defendant is not guilty by reason of insanity if a medical professional diagnoses them with a relevant mental defect and, at the time of the crime, they were unable to either:

  1. Appreciate the criminality of their conduct; or
  2. Conform their conduct to the requirements of the law

So, using the MPC test, a mental health professional must diagnose a person with a mental defect, and the person must prove either they did not know right from wrong or could not control an impulse that led to the criminal act.

Other Tests for Legal Insanity

The Model Penal Code test is much broader than the M'Naghten Rule and the Irresistible Impulse Test. The M'Naghten rule requires a defendant to show they did not have the substantial capacity to understand right from wrong. The Irresistible Impulse Test requires the inability to control an impulse even though the defendant knows it is wrong.

Do You Have a Defense Under the Model Penal Code Test? Talk to a Lawyer Today

Insanity defenses generally require pre-trial motions and specific factual findings regarding medical conditions. A qualified criminal defense attorney can walk you through this process. If you have more questions about insanity defenses or need professional representation, contact an experienced local criminal defense attorney today. An attorney can provide legal advice regarding the following:

Contact a criminal defense attorney today if the government has charged you with a crime.

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