Current Application of the Insanity Defense

The insanity defense is a legal defense to the commission of a crime. There's a desire to shield the mentally ill from the full brunt of the legal system. But there are also concerns about false claims of mental illness used to manipulate the criminal justice system.


Courts have struggled with developing a balance between protecting those suffering from mental disorders and protecting the public from those who would abuse the mental health system.

This article discusses the current application of the insanity defense. It also discusses the court requirements when a defendant claims to be innocent because of insanity.

Insanity Defense Background

From as early as the 12th century, the use of an insanity defense has essentially been a legal shield for those with mental illness. Under some circumstances, a mentally ill defendant found not guilty by reason of insanity is excused from the legal responsibility for their criminal behavior. This is true even though the person actually committed the crime or, in legal terminology, is "culpable" of the crime.

Throughout history, the standards surrounding the insanity defense have tightened dramatically, particularly after the John Hinckley verdict, which allowed President Ronald Reagan's attempted assassin to go to a psychiatric hospital rather than prison.

Differences Between the Insanity Defense, Competency To Stand Trial, and Diminished Capacity

All jurisdictions require that criminal defendants be competent to stand trial. This means defendants must understand the nature of the proceedings against them and be able to assist counsel in their defense.

A person found mentally incompetent to stand trial is usually hospitalized for treatment. The court will conduct regularly scheduled case reviews to see if the person has regained competency. If the defendant remains incompetent, they'll remain hospitalized at a mental institution.

But competency does not address a party's guilt or innocence. So, competency to stand trial is separate from asserting an affirmative insanity defense.

Many confuse insanity with diminished capacity. Diminished capacity results in a defendant pleading guilty to a lesser crime rather than being found not guilty due to a mental disease. The defendant accepts criminal responsibility but argues mitigating factors reduce the intent element.

For example, let's say you commit a crime while intoxicated. Use of the insanity defense by your criminal defense attorney will likely be unsuccessful. But they could argue you did not act with specific intent to cause a particular result due to your intoxication. This commonly applies when a defendant charged with murder ends up with a conviction for a lesser crime, such as manslaughter.

Tests Used To Determine Legal Insanity

A defendant's intent (mens rea) to commit the crime is a key element in most criminal cases. For example, common law burglary requires a defendant to break and enter an inhabited structure at night with intent to commit a felony, such as stealing personal property. Even in states with slightly different definitions of burglary, the intent to commit the crime is still a pivotal requirement.

Different jurisdictions have adopted several tests to evaluate a person's mental state at the time of the crime. When a defendant enters an insanity plea, they're telling the court they shouldn't be legally responsible because, at the time of the crime, they suffered from a defect of reason.

Four states do not allow criminal defendants to use the insanity defense to justify the criminal act. The following states don't use mental defects as a justification for criminal conduct:

  • Kansas
  • Idaho
  • Montana
  • Utah

Although criminal laws vary by state, the courts usually apply one of four tests (or a combination). The most common tests for insanity are:

  • The M'Naghten Rule: The defendant cannot distinguish right and wrong due to their state of mind.
  • The Irresistible Impulse Test: The defendant cannot control their impulses as a result of mental disease.
  • The Model Penal Code Test: The defendant lacks substantial capacity to act within the requirements of the law.
  • The Durham Rule: The defendant's mental disease caused the crime, even if they haven't received a prior clinical diagnosis.

Due to its vagueness, federal courts no longer use the Durham Rule. The only state that uses it is New Hampshire.

Burden of Proof for the Insanity Defense

The question of who has the burden of proof with an insanity defense has been controversial. Before the Hinckley case, most states placed the burden of proof on the state. The prosecutor had to prove that the defendant was not insane. But after the Hinckley verdict, the vast majority of states required the defense to prove that the defendant was insane.

In states where the burden is on the defense to prove insanity, the defense must show either clear and convincing evidence or by a preponderance of the evidence that the defendant is insane. In states where the burden is still on prosecutors to prove sanity, they must prove it beyond a reasonable doubt.

Commitment and Release Procedures

Defendants who successfully use the insanity defense are not simply released from custody. They're generally committed to mental hospitals, where their confinement may be longer than their prison terms would've been.

In the 1983 case of Jones v. United States, the Supreme Court backed this proposition. The Court ruled that the sentence criminal defendants would've received if convicted should have no bearing on the length of their commitment to a mental hospital.

After Hinckley, many states changed their commitment policies. A defendant found not guilty by reason of insanity must stay in a mental hospital for a certain period for evaluation following acquittal. Previously, there was no time specification. Several states also changed the burden of proof for release. Now, the burden is on defendants to prove rehabilitation.

The Federal Insanity Defense Reform Act

The Federal Insanity Defense Reform Act of 1984, codified at 18 U.S.C. section 17, provides: "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 of the wrongfulness of his acts. Mental disease or defect does not otherwise constitute a defense."

This Act was a response to the Hinckley verdict. It eliminated the Irresistible Impulse Test from the insanity defense under federal law. The Act also provided that "the defendant has the burden of proving the insanity defense by clear and convincing evidence." Previously, under federal law, the government had the burden of proving sanity.

Guilty but Mentally Ill

Finally, the Hinckley verdict accelerated the adoption of "guilty but mentally ill" verdicts by states.

Michigan adopted the first law allowing pleas and verdicts of guilty but mentally ill in 1975. Only three other states allow such verdicts:

  • Alaska
  • Georgia
  • Nevada

The "guilty but mentally ill" verdict allows the jury or court to find mentally ill defendants criminally liable. It requires them to receive psychiatric treatment while incarcerated. Alternatively, mentally ill defendants may get placed in a mental hospital. When they're well enough, they're moved to prison to serve their sentences.

Get Legal Help Understanding the Application of the Insanity Defense

Whether you wish to plead not guilty by reason of insanity or some other defense to criminal charges, you're going to need the help of a trained legal professional. Get help by contacting a skilled criminal defense attorney in your area.

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