Pleading insanity in court has become a trope in movies and television but the application of such a defense is much more complicated than advertised. For starters, insanity in a criminal case is treated as a legal term rather than a medical one. Understanding this distinction is important when considering your legal defense in a criminal case, as the nuance in definition can impact its success.

Due to being utilized as a legal defense, the definition and application changes and, in many cases, makes people uncomfortable. In fact, that legal definition could change depending on the state. For instance, someone who is found insane in New Jersey may receive a different verdict in New Hampshire or Pennsylvania, even though the states are not located too far away. The legal definitions can overlap with medical diagnoses of mental illnesses but they are not interchangeable.

In some cases, a person may be considered psychologically insane but it cannot be used as a defense. In other cases, the reverse can be true. While each state has their own definitions for insanity, there are three rules lawyers look at to determine if such a defense should be used.

M’Naghten Rule

Under this rule, the defendant can plead not guilty with insanity as a defense only if at the time of the alleged act, the defendant was unable to understand the nature of their actions due to being disturbed. Additionally, this defense can work if they did know the nature and quality of said actions but could not understand that it was wrong to act in such a way. This is the oldest rule for claims of insanity but still applies in over 20 states in the country.

Durham Rule

Under this rule, the defendant can be considered not guilty if their actions were the product of their mental illness. In other words, the crime would not have been committed if it had not been for their mental illness. This gives better coverage than the M’Naghten Rule since those with mental illness can understand they are wrong and still commit the crime purely because of their mental illness, such as an inability to control impulses.

Model Penal Code Rule

If, at the time of the crime, the behavior came as a result of a mental disease or the person was not able to understand the criminal intent or why it was wrong because of their state of mind, they can plead not guilty by reason of insanity. The American Law Institute wrote this rule to bridge the gap between the narrow M’Naghten Rule and the broad Durham Rule.

Unlike in Hollywood, someone cannot simply claim they are insane and get an evaluation. If you or a loved one committed a crime due to a mental illness, contact us today. We understand how criminal defense works in every situation and can tailor your defense to your specific circumstances.

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