When Does the Insanity Defense Apply to Criminal Cases?

Mental health problems are indisputably a factor that frequently contributes to crime. According to data from the American Psychological Association and the National Alliance on Mental Illness, people in prison in the U.S. are more than twice as likely to suffer from a significant mental disorder than the population at large.

Violent impulses may be exacerbated by various mental health conditions, including schizophrenia, personality disorders, and substance abuse problems. Stress, isolation, such as what many of us experienced during Covid lockdowns, financial problems and anxiety, and abuse can also be factors. In a particularly miserable state, any of us might experience a “breakdown” and make a horrible decision, perhaps without even thinking about it.

But if you commit a crime while in the throes of a full-blown mental health crisis, you might be surprised to learn that the insanity defense may not be your best option. While popular media makes pleading insanity in a criminal case sound relatively easy, the reality is far more complex. In fact, only about 1 percent of all criminal cases in the U.S. involve an insanity plea.

Why so few? Well, there is a long list of reasons.

Here are some things that might be useful to know about how and when you can use the insanity defense. While we can’t give you legal advice for your specific situation here (you would have to contact our office to obtain that), we can provide you with some general information to guide you.

Not every state allows you to use the insanity defense, and for those that do, the rules can vary. Four states — Kansas, Utah, Montana, and Idaho — do not allow defendants to plead insanity at all. In federal cases, you can plead insanity if you can show by “clear and convincing evidence” that you were “unable to appreciate the nature and quality or the wrongness” of the acts at the time when they were committed because of severe mental illness. This is a very high threshold to meet.

If you’re allowed to plead insanity, there are four different types of defenses you might be able to use, depending on the circumstances and the specifics of the state’s laws. Those are the M’Naghten defense, the irresistible impulse defense, the substantial capacity defense, and the Durham defense.

  1. The M’Naghten defense has two elements: The defendant must have suffered from a mental defect or disease at the time of the crime. The defendant also must not have known that the nature or quality of the criminal act was wrong because of the mental defect or disease.
  2. The irresistible impulse defense also has two elements: That the defendant was suffering from a mental defect or disease at the time of the crime, and the defendant could not control his or her conduct because of that mental defect or disease.
  3. The substantial capacity defense is similar to the M’Naghten defense, but somewhat softer in its required elements. The defendant must lack substantial capacity (rather than total capacity) for appreciating the criminality of conduct for reasons of mental illness or defect.
  4. The Durham rule is perhaps the broadest. It allows defendants to be excused of criminal conduct if the acts resulted from a mental disease or defect. In practice, however, it is difficult to apply, and hardly any state uses it.

There are other defenses that are not full-blown insanity pleas, but could reduce your criminal liability. These include the diminished capacity defense, which may, for instance, reduce a first-degree murder charge to second-degree murder or manslaughter if the defendant was found to be lacking in first-degree murder intent because of mental health issues.

Competency to stand trial is not the same thing as an insanity defense. If a court finds you are not competent to stand trial, that does not excuse you from criminal liability. It just means that your case will not move forward until you are restored to competency. This could mean that you are housed at a treatment facility or provided with psychiatric medication, putting you in a state where you can understand the nature of the proceeding and the case can continue.

In some states, you can be found mentally ill but still guilty. This does not excuse you from criminal conduct. Instead, this means that you will be required to undergo mental health treatment as part of your sentence.

If you are found not guilty by reason of insanity, you may still lose your freedom. In federal cases and in many states, you will be committed to a mental health facility if you are successful in your insanity plea. Some states will have further hearings to decide whether you should be committed.

Temporary insanity pleas do happen, but they are extremely rare. While in courtroom dramas, we often see people claim temporary insanity where there are crimes of passion, there is a very high bar to establishing this in court. Usually, this requires the testimony of mental health experts, and evidence of insanity at the time of the incident.

Although prosecutors have the burden of proving you committed a crime, you have the burden of proving you were not sane. Insanity is an affirmative defense, which means that you, as the defendant, are required to provide evidence establishing these facts. That’s why having an experienced attorney representing you in these matters is extremely important.

Although insanity defenses are difficult to make, some high-profile defendants have been successful. Those who have been successful include John Hinckley Jr., who shot former U.S. President Ronald Reagan in a failed assassination attempt in 1981. Hinckley Jr., who demonstrated that he attempted the killing largely because of a deranged obsession with actress Jodie Foster, was found not guilty by reason of insanity and committed to a mental hospital for more than 40 years.

Another successful insanity plea was made by Lorena Bobbitt, who infamously cut off her husband’s penis with a kitchen knife in 1993. She was found not guilty of criminal charges based on the exceedingly rare temporary insanity plea. Lorena Bobbitt showed that she had endured years of abuse, rape, and other miseries during her marriage to John Bobbitt, and the accumulation of her trauma pushed her to the brink.