A criminal defendant who is found legally insane (or "not guilty by reason of insanity") cannot be held accountable for crimes resulting from the condition. After all, prosecutors are required to show a defendant's willful intent in order to prove guilt for most criminal charges. State courts use one of several established legal tests to determine whether someone was insane at the time of the incident or simply faking it. These include the M'Naghten Rule; the Irresistible Impulse test; the Durham Rule; and the Model Penal Code test.
This article focuses on the Model Penal Code (or MPC) legal standard for insanity. See Insanity Defense; Current Application of the Insanity Defense; and Status of the Insanity Defense for more information.
Model Penal Code Test: Basics
Using the MPC test, a criminal defendant must be found not guilty by reason of insanity if he is diagnosed with a relevant mental defect (for example, severe mental retardation or schizophrenia disorder) and at the time of the incident was unable to either:
Therefore, using the MPC test, a legally insane individual must have been diagnosed with a mental defect (typically by a court-appointed mental health professional) and either did not know right from wrong or lacked the ability to control an impulse that led to the incident.
The MPC test was widely adopted in the 1970s since it allowed more flexibility than other tests at the time. However, it fell out of favor when John Hinckley, Jr. was found not guilty by reason of insanity (based on the MPC test) for his attempted assasination of President Ronald Reagan in 1981. Soon after the trial, the federal government and many states reverted back to the stricter N'Naghten rule.
It is still used in 18 jurisdictions, including the District of Columbia; Illinois; and New York. See The Insanity Defense Among the States for more details.
Example of Legal Insanity Under the MPC Test
John, who has been diagnosed with severe schizophrenia, was charged with assault and battery after beating up a stranger at a bus stop. As a result of his condition, he occasionally hears voices urging him attack certain individuals. John knows it was wrong to attack this person, but claims he was unable to control the impulse to do so.
A court using the MPC test likely would find him not guilty by reason of insanity because he was unable to conform his conduct to the law prohibiting assault and battery.
How MPC Compares to Other Insanity Tests
The Model Penal Code test is much broader than the M'Naghten Rule and the Irresistible Impulse Test. Legal insanity requires the inability to understand right from wrong under the M'Naghten rule, while the Irresistible Impulse Test requires the inability to control an impulse. The MPC rule asks whether defendants are able to fully understand the criminality of their conduct or able to conform their conduct to the law, combining these two elements.
It also requires that the mental disease or defect be diagnosed by a licensed mental health professional. In this way, it incorporates the main element required by the Durham Rule.
If you have additional questions about the Model Penal Code test for legal insanity or need representation, consider speaking with a criminal defense lawyer in your area.
Your Next Steps: Get a Free Case Review
Under any test used, an insanity defense is going to require pre-trial motions and specific factual findings regarding medical conditions. A qualified criminal defense attorney can walk you through this process and let you know whether this is a workable defense. If you have more questions about insanity defenses or would just like a free review of your case, reach out to an attorney near you today.