Pleading Insanity in a Criminal Case

A successful insanity defense usually results in many years of mandatory treatment in a psychiatric hospital, not a free ride out of prison.

Updated by , Attorney · Mitchell Hamline School of Law
Updated 11/28/2023

The insanity defense is a controversial and often misunderstood part of the criminal system. In fact, it's rarely raised and very rarely successful. It's not the "get out of jail free" card that some believe it to be.

What Does It Mean to Plead Insanity?

When defendants plead not guilty by reason of insanity (NGRI), they are asserting an affirmative defense—that is, they admit that they committed a criminal act, but seek to excuse their behavior by reason of mental illness that satisfies the definition of legal insanity. People who are adjudged to have been insane at the time they committed a crime are neither legally nor morally guilty.

Pleading insanity isn't the same as pleading guilty. A jury will typically decide if the defendant has proven their insanity claim, which is a process similar to many other affirmative defenses. When a defendant raises the insanity defense, a jury may reach a verdict of guilty, not guilty, or not guilty by reason of insanity.

When Can the Insanity Defense Be Used?

Defendants must inform prosecutors prior to trial if they plan to rely on an insanity defense. Typically, defense lawyers and prosecutors each obtain their own psychiatrists to examine a defendant and testify at trial. Judges appoint government-paid psychiatrists for indigent defendants.

Defendants typically have the burden of convincing judges or juries by either a preponderance of the evidence or by the tougher standard of clear and convincing evidence that they were insane at the time they committed a criminal act. Evidence rules forbid defense psychiatrists from testifying to an opinion that a defendant was legally insane at the time a crime was committed. They can only provide a medical diagnosis concerning a defendant's mental illness.

Is Competency to Stand Trial the Same as Pleading Insanity?

No, the two are related concepts but very different procedures. Pleading insanity looks at the defendant's mental capacity at the time of the crime. Competency to stand trial applies at the time of the trial.

All defendants must be competent to stand trial. It's a constitutional requirement. Defendants must be able to assist in their defense, meaning they must understand the nature of the criminal proceedings. A judge (not a jury) will decide whether a defendant is competent to stand trial.

If a defendant is deemed not competent, the judge suspends the trial and typically commits the defendant to a mental health facility for treatment. Once the defendant regains the capacity to stand trial, the proceedings resume.

How Is Insanity Proved in Court?

As noted above, it's usually up to the defendant to prove insanity. The American justice system has struggled with the appropriate insanity test since the 1800s. And it continues to struggle for a method to distinguish offenders whose mental illness is so severe that society should deem them not morally responsible for their behavior, from offenders whose actions, while perhaps objectively irrational, nevertheless merit punishment. Over the decades, five tests have developed to "define" legal insanity.

M'Naghten Test

Many states define legal insanity according to the M'Naghten test, developed in an 1843 English case. An offender is insane under this test if mental illness prevents the offender from knowing the difference between right and wrong.

Irresistible Impulse Test

Some states supplement the M'Naughten test with the irresistible impulse rule, under which offenders are insane if a mental disorder prevents them from resisting the commission of an illegal act that they know is wrong.

Model Penal Code or American Law Institute (ALI) Test

The Model Penal Code or ALI test is a revised version of the M'Naughten and irresistible impulse tests. Under the ALI test, a person is not responsible for their criminal acts if, at the time of the crime, they lacked substantial capacity to either:

  • appreciate the criminality of their conduct, or
  • conform their conduct to the law.

Durham or Product Test

Only used in New Hampshire, the product test provides that a person should be excused from criminal liability if their unlawful conduct was the product of a mental disease or defect. The test does not define "mental disease or defect."

Federal Insanity Test

The federal insanity defense uses various aspects of the other four tests. It's found in the U.S. Code. "It is an affirmative defense to a prosecution under any Federal statute that, at the time of the commission of the acts constituting the offense, the defendant, as a result of a severe mental disease or defect, was unable to appreciate the nature and quality or the wrongfulness of his acts." (18 U.S.C. § 17.)

What Happens After an Insanity Plea or Not Guilty by Reason of Insanity Verdict?

Defendants found not guilty by reason of insanity are rarely set free. Instead, they are almost always confined in mental health institutions. They may remain confined for a longer period of time than had they been found guilty and sentenced to a term in prison. States may compel defendants adjudged insane to remain in a mental health institution until they convince a judge that they are no longer legally insane.

Famous Insanity Defense Cases

Studies show that defendants offer an insanity defense in less than 1% of all felony cases and, within this 1%, are successful only about 25% of the time. Despite these low, low rates, insanity plea cases often receive intense media coverage—making it appear that NGRI verdicts are much more common than they really are. Some famous cases are described below.

John Hinckley, Jr. attempted to assassinate President Ronald Reagan. A jury found Hinckley not guilty by reason of insanity. He spent 35 years in a psychiatric hospital and 41 years under court supervision. In June 2022, a judge granted him unconditional release.

Andrea Yates drowned all five of her children in a bathtub, one by one. She had been treated previously for postpartum depression and psychosis. A psychiatrist testified that Yates believed killing her children would save them from Satan. A jury found her not guilty by reason of insanity. She remains hospitalized.

James Holmes killed 12 people and wounded 70 more when he opened fire in a Colorado movie theater. He pleaded not guilty by reason of insanity, which the jury rejected. A judge sentenced him to 12 consecutive life sentences (3,318 years in prison).

Talk to a Defense attorney
We've helped 95 clients find attorneys today.
There was a problem with the submission. Please refresh the page and try again
Full Name is required
Email is required
Please enter a valid Email
Phone Number is required
Please enter a valid Phone Number
Zip Code is required
Please add a valid Zip Code
Please enter a valid Case Description
Description is required

How It Works

  1. Briefly tell us about your case
  2. Provide your contact information
  3. Choose attorneys to contact you