Insanity Defense

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A defense asserted by an accused in a criminal prosecution to avoid liability for the commission of a crime because, at the time of the crime, the person did not appreciate the nature or quality or wrongfulness of the acts.

The insanity defense is used by criminal defendants. The most common variation is cognitive insanity. Under the test for cognitive insanity, a defendant must have been so impaired by a mental disease or defect at the time of the act that he or she did not know the nature or quality of the act, or, if the defendant did know the nature or quality of the act, he or she did not know that the act was wrong. The vast majority of states allow criminal defendants to invoke the cognitive insanity defense.

Another form of the insanity defense is volitional insanity, or irresistible impulse. A defense of irresistible impulse asserts that the defendant, although able to distinguish right from wrong at the time of the act, suffered from a mental disease or defect that made him or her incapable of controlling her or his actions. This defense is common in crimes of vengeance. For example, suppose that a child has been brutally assaulted. If an otherwise conscientious and law-abiding mother shoots the perpetrator, the mother may argue that she was so enraged that she became mentally ill and incapable of exerting self-control. Very few states allow the volitional insanity defense.

The insanity defense should not be confused with incompetency. Persons who are incompetent to stand trial are held in a mental institution until they are considered capable of participating in the proceedings.

The insanity defense also should be kept separate from issues concerning mental retardation. The U.S. Supreme Court ruled in 2002 in atkins v. virginia, 536 U.S. 304, 122 S. Ct. 2242, 153 L. Ed. 2d 335 (2002) that the execution of mentally retarded criminals constituted "cruel and unusual punishment" and that it was prohibited by eighth amendment. But if a person is acquitted by reason of insanity, execution is not an option.

The insanity defense reflects the generally accepted notion that persons who cannot appreciate the consequences of their actions should not be punished for criminal acts. Most states regulate the defense with statutes, but a few states allow the courts to craft the rules for its proper use. Generally, the defense is available to a criminal defendant if the judge instructs the jury that it may consider whether the defendant was insane when the crime was committed. The judge may issue this instruction if the defendant has produced sufficient evidence at trial to justify the theory. Sufficient evidence invariably includes expert testimony by psychologists and psychiatrists.

When invoking insanity as a defense, a defendant is required to notify the prosecution. In some states, sanity is determined by the judge or jury in a separate proceeding following the determination of guilt or innocence at trial. In other states, the defense is either accepted or rejected in the verdict of the judge or jury. Even if evidence of insanity does not win a verdict of not guilty, the sentencing court may consider it as a mitigating factor.


"Complete madness" was first established as a defense to criminal charges by the common-law courts in late-thirteenth-century England. By the eighteenth century, the complete madness definition had evolved into the "wild beast" test. Under that test, the insanity defense was available to a person who was "totally deprived of his understanding and memory so as not to know what he [was] doing, no more than an infant, a brute, or a wild beast" (Feigl 1995, 161).

Colin Ferguson

Colin Ferguson was convicted in March 1995 for crimes associated with a massacre in Long Island, New York, on December 7, 1993. Ferguson killed six persons and injured nineteen after opening fire with an automatic pistol on a crowded commuter train.

Ferguson's trial was marked with controversy. He discharged his court-appointed attorneys, who believed him mentally incompetent to stand trial, and was allowed by the judge to act as his own attorney. He dropped the insanity defense prepared by his attorneys and argued that a mysterious gunman had committed the shootings.

His bizarre courtroom behavior appeared to contradict the judge's conclusion that Ferguson was competent to stand trial. Though many witnesses identified Ferguson as the gunman, he insisted a white man had taken the gun from his bag while he slept, shot the passengers, and then escaped, leaving Ferguson, who is black, to take the blame. During the trial he asserted that he had been charged with ninety-three counts only because the crime occurred in 1993.

Attorneys Ronald L. Kuby and william m. kunstler, whom Ferguson had discharged, had asked the judge before trial to find that Ferguson's paranoia and delusional state made him mentally incompetent to stand trial. Yet Ferguson refused to be examined by either prosecution or defense psychiatrists, believing he was not insane. The judge allowed Ferguson to stand trial, believing he could understand the nature of the charges against him and could assist in his own defense.

By 1840, most jurisdictions had refined the wildbeast test to cognitive insanity and supplemented that with irresistible impulse insanity. However, in 1843, a well-publicized assassination attempt in England caused Parliament to eliminate the irresistible impulse defense. Daniel M'Naghten, operating under the delusion that Prime Minister Robert Peel wanted to kill him, tried to shoot Peel but shot and killed Peel's secretary instead. Medical testimony indicated that M'Naghten was psychotic, and the court acquitted him by reason of insanity (M'Naghten's Case, 8 Eng. Rep. 718 [1843]). In response to a public furor that followed the decision, the House of Lords ordered the Lords of Justice of the Queen's Bench to craft a new rule for insanity in the criminal law.

What emerged became known as the m'naghten rule. This rule migrated to the United States within a decade of its conception, and it stood for the better part of the next century. The intent of the M'Naghten rule was to abolish the irresistible-impulse defense and to limit the insanity defense to cognitive insanity. Under the M'Naghten rule, insanity was a defense if

at the time of the committing of the act, the party accused was labouring under such a defect of reason, from a disease of the mind, as not to know the nature and quality of the act he was doing; or, if he did know it, that he did not know he was doing what was wrong.

Through the first half of the twentieth century, the insanity defense was expanded again. Courts began to accept the theories of psychoanalysts, many of whom encouraged recognition of the irresistible-impulse defense. Many states enacted a combination of the M'Naghten rule supplemented with an irresistible-impulse defense, thereby covering both cognitive and volitional insanity.

The insanity defense reached its most permissive standard in Durham v. United States, 214 F. 2d 862 (D.C. Cir. 1954). The Durham rule excused a defendant "if his unlawful act was the product of mental disease or mental defect." The Durham rule was lauded by the mental health community as progressive because it allowed psychologists and psychiatrists to contribute to the judicial understanding of insanity. But it was also criticized for placing too much trust in the opinions of mental health professionals. Within seven years of its creation, the rule had been explicitly rejected in 22 states. It is used only in New Hampshire.

Is There a Need for the Insanity Defense?

Though the insanity defense is rarely invoked in criminal trials, it remains a controversial issue. Legislators and the public generally question the need for the defense after a defendant in a highly publicized murder case is found not guilty by reason of insanity. For example, when John Hinckley successfully used the defense after shooting President ronald reagan to impress the actress Jodie Foster, there was a public outcry. Legal and medical commentators have divided opinions about the need for the insanity defense.

Those who wish to retain it note that forty-eight of the fifty states have some type of insanity defense. This, they claim, is evidence of the need for such a defense. The public is given a distorted view of who uses the defense and how it is employed. In fact about one percent of criminal defendants invoke the defense. More important, criminals rarely "beat the rap" by pleading insanity. When an insanity defense is employed, it means the defendant admits committing the criminal behavior and is now seeking a not guilty verdict on the basis of his state of mind. If the jury does not agree, the defendant will be convicted, and generally will serve a longer sentence than will someone convicted of the same crime who has not pleaded insanity.

Juries find for only about 20 percent of the defendants who plead insanity. Even this figure does not reflect the reality that many insanity pleas are the result of plea bargains, which indicates that prosecutors agree that such pleas are sometimes appropriate.

Finally, the fact that most highly publicized cases involve murder disguises the true demographics: 60 to 70 percent of insanity pleas are for crimes other than murder. They range from assault to shoplifting.

All these myths have led to the belief that criminals can avoid punishment by claiming insanity. The truth is that the insanity defense is a risky one at best.

Apart from combating these myths, advocates of the insanity defense contend that a fundamental principle of criminal law is at stake. The insanity defense is rooted in the belief that conviction and punishment are justified only if the defendant deserves them. The basic pre-condition for punishment is that the person who committed the criminal behavior must have responsibility as a moral agent. When a person is so mentally disturbed that her irrationality or compulsion is impossible to control, that person lacks responsibility as a moral agent. It would be unfair to punish a person in such an extreme condition.

Based on this argument, proponents of the insanity defense do not support its application to a person who willingly consumes a powerful hallucinogen and then commits a criminal act. Nor would they allow its application to a person who is able to control a mental disorder through medication but fails to do so. But they do support the defense for a person who unwittingly consumes hallucinogens and then commits a crime.

Some opponents attack the insanity defense for confusing psychiatric and legal concepts, in the process undermining the moral integrity of the law. Both sides agree that the word insane is a legal, not medical, term. It is too simplistic to describe a severely mentally ill person merely as insane, and the vast majority of people with a mental illness would be judged sane if current legal tests for insanity were applied. The legal tests for insanity, moreover, require that a defendant's mental condition become so impaired that the fact finder may conclude the person has lost his or her free will. Because free will is not a concept that can be explained in medical terms, it may be impossible for a psychiatrist to determine if the mental impairment affected the defendant's capacity for voluntary choice. Without a way to measure insanity, it makes no sense to let prosecution and defense psychiatrists spar over the issue. A jury's decision based on psychiatrists' opinions may be grounded on unreliable evidence.

Another major argument against the insanity defense challenges its supposed moral basis. Critics contend that modern criminal law is concerned more with the consequences of crime and less with moral imperatives. If a person commits a criminal act, that person should be convicted. Mental illness can be taken into consideration at the time of sentencing. This line of reasoning supports laws that several states have adopted, which abolish the insanity defense and replace it with a new verdict of guilty but insane. This verdict carries a criminal penalty. It allows the judge to determine the length of imprisonment, which occurs in a hospital prison, and shifts the burden to the defendant to prove he is no longer dangerous or mentally ill in order to be released.

Finally, critics argue that the insanity plea is a rich person's defense. Only wealthy defendants can retain high-priced psychiatric experts. Persons represented by public defenders are usually afforded a psychiatric examination for the defense, but they may not get the same quality of exam, nor are they typically able to hire more than one examiner. Because a two-tiered criminal justice system is morally repugnant, critics contend that the insanity defense must be abolished.

In 1964, the American Law Institute (ALI) began to reassess the insanity defense in the course of promoting a new model penal code. What emerged from the Model Penal Code Commission was a compromise between the narrow M'Naghten test and the generous Durham rule. The ALI test provided that a person was not responsible for criminal conduct if, at the time of the act, the person lacked "substantial capacity" to appreciate the conduct or to conform the conduct to the rule of law. The ALI test provided for both cognitive and volitional insanity. It also required only a lack of substantial capacity, less than complete impairment. The ALI version of the insanity defense was adopted by more than half the states and all but one federal circuit.

Several years later, another dramatic event led to another round of restrictions on the insanity defense. In 1981, John W. Hinckley, Jr., attempted to assassinate President ronald reagan. Hinckley was prosecuted and acquitted of all charges by reason of insanity, and a resulting public outcry prompted Congress to enact legislation on the issue. In 1984, Congress passed the Insanity Defense Reform Act (Insanity Act) (18 U.S.C.A. § 17 [1988]) to abolish the irresistible-impulse test from federal courts. Initially, Reagan had called for a total abolition of mental illness as a defense to criminal charges, but his administration backed down from this position after intense lobbying by various professional organizations and trade associations.

The Insanity Act also placed the burden on the defendant to prove insanity. Before the Insanity Act, federal prosecutors bore the burden of proving the defendant's sanity beyond a reasonable doubt.

Most states joined Congress in reevaluating the insanity defense after Hinckley's acquittal. The legislatures of these states modified and limited the insanity defense in many and varied ways. Some states shifted the burden of proof, and some limited the applicability of the defense in the same manner as Congress did. A few states abolished the defense entirely. Chief Justice william h. rehnquist, of the U.S. Supreme Court, opined in a dissent that it is "highly doubtful that due process requires a State to make available an insanity defense to a criminal

defendant" (Ake v. Oklahoma, 470 U.S. 68, 105 S. Ct. 1087, 84 L. Ed. 2d 53 [1985]).


When a party successfully defends criminal charges on a ground of insanity, the consequences vary from jurisdiction to jurisdiction. Usually, the defendant is committed to a mental institution. On the average, a defendant found not guilty by reason of insanity and committed to a mental institution is confined for twice as long as is a defendant who is found guilty and sent to prison. Very few acquitted insanity defendants are given supervised release, and even fewer are released directly following their verdict.

The detention of an insanity acquittee is limited by law. The acquittee must be allowed periodic review in the mental institution, to determine whether continued treatment is necessary. In addition, a hospital facility may not hold an insanity acquittee indefinitely merely because the acquittee has an antisocial personality (Foucha v. Louisiana, 504 U.S. 71, 112 S. Ct. 1780, 118 L. Ed. 2d 437 [1992]).

The procedural framework in Massachusetts illustrates the consequences that come with the insanity defense. Under chapter 123, section 16, of the Massachusetts General Laws Annotated, the court may order a person found not guilty by reason of insanity (an insanity acquittee) to be hospitalized for 40 days for observation and examination. During this period, the district attorney or the superintendent of the mental hospital may petition the court to have the insanity acquittee committed to the hospital. If the judge orders the commitment, the acquittee is placed in the hospital for six months.

After the first six months have expired, the commitment is reviewed again, and then once a year thereafter. If the superintendent of the mental health facility moves to discharge the acquittee, the district attorney must respond with any objections within 30 days of notice from the superintendent. The mental health facility is authorized to restrict the movement of criminal defendants and insanity acquittees, so a commitment is tantamount to incarceration.

Defendants' Rights

When pleading insanity, a defendant might not want to present the best possible image at trial. In Riggins v. Nevada, 504 U.S. 127, 112 S. Ct. 1810, 118 L. Ed. 2d 479 (1992), defendant David Riggins was charged with robbing and murdering Las Vegas resident Paul Wade. After being taken into custody, Riggins complained that he was hearing voices in his head and that he was having trouble sleeping. A psychiatrist at the jail prescribed 100 milligrams per day of Mellaril, an antipsychotic drug. By the time of trial, the psychiatrist was prescribing 800 milligrams per day of Mellaril.

Just before trial, Riggins's attorney moved the court to suspend administration of the Mellaril. Riggins was pleading not guilty by reason of insanity, and his attorney wanted the jury to see Riggins in his natural state. According to one psychiatrist, Dr. Jack Jurasky, Riggins "would most likely regress to a manifest psychosis and become extremely difficult to manage" if he were taken off Mellaril.

The court denied the motion, and Riggins was convicted and sentenced to death. The Nevada Supreme Court affirmed Riggins's convictions and death sentence. On appeal to the U.S. Supreme Court, the convictions were reversed. According to the high court, Nevada had violated Riggins's due process rights under the Sixth and Fourteenth Amendments. In the absence of evidence that the treatment was medically appropriate and essential for Riggins's own safety or the safety of others, and without an exploration of less intrusive alternatives, the trial court had erred by denying Riggins's liberty interest in freedom from antipsychotic drugs.

According to the Court, the administration of the Mellaril jeopardized a number of Riggins's trial rights. Not only was it possible that the Mellaril had affected Riggins's outward appearance, and thus his defense, but the high daily dosage of Mellaril also might have affected Riggins's testimony, his ability to communicate with his attorney, and his ability to follow the proceedings. Although the defense had been allowed to present expert testimony on the nature of Riggins's mental condition, the Court concluded that the compromise of Riggins's trial rights was reversible error.

Uses and Abuses

Victims of abuse often allege temporary insanity in defending their own violent behavior. For example, in 1994, Virginia resident Lorena Bobbitt, charged with severing her husband's penis with a knife, was acquitted of assault charges on the ground of temporary insanity. At trial, Bobbitt testified that her husband had abused her physically and emotionally.

Critics complain that the insanity defense is abused by defense attorneys, who use it to free the perpetrators of deliberate criminal acts. However, 95 percent of all persons found not guilty by reason of insanity are detained in hospitals, and in practice, the insanity defense is rarely invoked and rarely successful. The insanity defense is used by defendants in only one percent of all felony cases, and it results in acquittal in only one-quarter of those cases.

Psychopaths and Sociopaths

When most people hear about the insanity defense, they automatically assume that it can be used applied to people commonly referred to as psychopaths and sociopaths. While traditionally there has been a small degree of difference between these two classifications, the American Psychiatric Associations most recent Diagnostic and Statistical Manual—Fourth Edition ("DSMIV") groups sociopathy and psychopathy under the heading "antisocial personality disorder." The DSM-IV lays out a limited and concise set of diagnostic criteria on which to base the diagnosis of antisocial personality disorder.

According to the DSM-IV, antisocial personality disorder is characterized by pervasive pattern of disregard for, and violation of, the rights of others occurring since age 18, as indicated by three (or more) of the following: (1) failure to conform to social norms with respect to lawful behaviors as indicated by repeatedly performing acts that are grounds for arrest; (2) deceitfulness, as indicated by repeated lying, use of aliases, or conning others for personal profit or pleasure; (3) impulsivity or failure to plan ahead; (4) irritability and aggressiveness, as indicated by repeated physical fights or assaults; (5) reckless disregard for safety of self or others; (6) consistent irresponsibility, as indicated by repeated failure to sustain consistent work behavior or to honor financial obligations; (7) lack of remorse, as indicated by being indifferent to, or rationalizing, having hurt, mistreated, or stolen from another.

However it is defined, many in the legal community doubt whether the insanity defense covers this kind of behavior at all. The ALI's Model Penal Code test of insanity states that "the terms mental disease or defect do not include an abnormality that is manifested only by repeated criminal or otherwise antisocial conduct." In other words, the criteria laid down by the DSMIV for antisocial personality disorder would not allow for a claim of insanity under the Model Penal Code, the most widely used insanity test, or in other insanity tests used by states. Thus, sociopaths and psychopaths, while perceived as insane by most people, could likely not use the insanity defense as a defense in a court of law.

For this reason, most celebrated serial killers such as John Wayne Gacy and Ted Bundy, as well as persons whose mental stability seems to be of a questionable nature, such as Ted Kaczynski, have seen their insanity pleas fail or have never used the defense. In fact, in recent years, only Hinckley and Bobbitt are among celebrated cases who have used the defense successfully. For criminals with antisocial personality disorder, the insanity plea simply does not apply.

further readings

American Psychiatric Association. 1994. Diagnostic and Statistical Manual of Mental Disorders—Fourth Edition. Washington D.C.: American Psychiatric Press.

Bing, Jonathan L. 1996. "Protecting the Mentally Retarded from Capital Punishment: State Efforts Since Penry and Recommendations for the Future." New York University Review of Law and Social Change 22.

Campbell, Emily. 1990. "The Psychopath and the Definition of 'Mental Disease or Defect' Under the Model Penal Code Test of Insanity: A Question of Psychology or a Question of Law?" Nebraska Law Review 69.

Ellickson, Robert C. 1996. "Controlling Chronic Misconduct in City Spaces: Of Panhandlers, Skid Rows, and Public-Space Zoning." Yale Law Journal 105.

Giorgi-Guarnieri, Deborah, et. al. 2002. "Practice Guideline; Forensic Psychiatric Evaluation of Defendants Raising the Insanity Defense." Journal of the American Academy of Psychiatry and the Law 30 (June).

Kuby, Ronald L., and William M. Kunstler. 1995. "So Crazy He Thinks He Is Sane: The Colin Ferguson Trial and the Competency Standard." Cornell Journal of Law and Public Policy 5.

LaFond, John Q., and Mary L. Durham. 1992. Back to the Asylum: The Future of Mental Health Law and Policy in the United States. New York: Oxford Univ. Press.

Melville, John D., and David Naimark. 2002. "Punishing the Insane: The Verdict of Guilty but Mentally Ill." Journal of the American Academy of Psychiatry and the Law 30 (December): 553–5.

Morse, Stephen J. 1985. "Excusing the Crazy." Southern California Law Review 58.

Rogers, Richard, and and Daniel Shuman. 2000. Conducting Insanity Evaluations. 2d ed. New York: Guilford Press.

Semrau, Stanley, and Judy Gale. 2002. Murderous Minds on Trial: Terrible Tales from a Forensic Psychiatrist's Case Book. Toronto, Tonawanda, N.Y.: Dundurn Press.


M'naghten Rule.

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Insanity Defense

Sections within this essay:

The M'Naghten Rule
The Irresistible Impulse Test
The Durham Rule
The American Law Institute's Model Penal Code Test
The Hinckley Trial
Current Application of the Insanity Defense
Burden of Proof
Commitment and Release Procedures
Distinction Between the Insanity Defense and Competency to Stand Trial
The Federal Insanity Defense Reform Act
Guilty but Mentally Ill

Status of the Insanity Defense in Criminal Law
The Insanity Defense Among the States
Additional Resources
American Bar Association Criminal Justice Section
American Psychological Association (APA)
Association of Federal Defense Attorneys


Although the insanity defense is probably the most controversial of all criminal defense strategies, it is also, somewhat ironically, one of the least used. On many occasions when it has been used, particularly in the much-publicized 1984 acquittal of John W. Hinckley, Jr. for the attempted assassination of President Ronald Reagan, the insanity defense has tended to provoke public debate.

The insanity defense asserts that a criminal defendant should not be found guilty due to the defendant's insanity. The theory behind the defense is that a person who is insane lacks the intent required to perform a criminal act because the person either does not know that the act is wrong or cannot control his or her actions even when the person understands that the act is wrong. This theory is controversial because insanity itself is difficult to define, and the circumstances in which insanity can be used to excuse criminal responsibility are difficult to characterize.

The insanity defense has existed since the twelfth century, but initially it was not considered an argument for the defendant to be found not guilty. Instead, it was a way for a defendant to receive a pardon or a way to mitigate a sentence. The idea that insanity could bar the conviction of a defendant arose in the early nineteenth century in The Medical Jurisprudence of Insanity by an influential scholar named Isaac Ray, as well as in the seminal decision in England called the M'Naghten case.

The M'Naghten Rule

In 1843, Daniel M'Naghten, an Englishmen who was apparently a paranoid schizophrenic under the delusion that he was being persecuted, shot and killed Edward Drummond, Secretary to British Prime minister Sir Robert Peel. M'Naghten believed that Drummond was Peel. To the surprise of the nation, M'Naghten was found not guilty on the grounds that he was insane at the time of his act. The subsequent public outrage convinced the English House of Lords to establish standards for the defense of insanity, the result subsequently referred to as the M'Naghten Rule.

The M'Naghten Rule provides as follows: "Every man is to be presumed to be sane, and … that to establish a defense on the ground of insanity, it must be clearly proved that, at the time of the committing of the act, the party accused was laboring under such a defect of reason, from disease of mind, and not to know the nature and quality of the act he was doing; or if he did know it, that he did not know he was doing what was wrong."

The test to determine if a defendant can distinguish right from wrong is based on the idea that the defendant must know the difference in order to be convicted of a crime. Determining a defendant's ability to do so may seem straightforward enough, but dilemmas often arise in cases in which the M'Naghten standard is used. For instance, some issues focus on whether a defendant knew that his or her criminal acts were wrong or whether he or she knew that laws exist that prohibit these acts.

Criticism of the M'Naghten test often focuses on the test's concentration on a defendant's cognitive abilities. Questions also crop up about how to treat defendants who know their acts are against the law but who cannot control their impulses to commit them. Similarly, the courts need to determine how to evaluate and assign responsibility for emotional factors and compulsion. Additionally, because of the rule's inflexible cognitive standard, it tends to be difficult for defendants to be found not guilty by reason of insanity. Despite these complications, M'Naghten has survived and is currently the rule in a majority of states with regard to the insanity defense (sometimes combined with the Irresistible Impulse Test, discussed below).

The Irresistible Impulse Test

In response to criticisms of the M'Naghten Rule, some legal commentators began to suggest expanding the definition of insanity to include more than a cognitive element. Such a test would encompass not only whether defendants know right from wrong but also whether they could control their impulses to commit wrong-doing. The Irresistible Impulse Test was first adopted by the Alabama Supreme Court in the 1887 case of Parsons v. State. The Alabama court stated that even though the defendant could tell right from wrong, he was subject to "the duress of such mental disease [that] he had … lost the power to choose between right and wrong" and that "his free agency was at the time destroyed," and thus, "the alleged crime was so connected with such mental disease, in the relation of cause and effect, as to have been the product of it solely." In so finding, the court assigned responsibility for the crime to the mental illness despite the defendant's ability to distinguish right from wrong.

The Irresistible Impulse Test gained acceptance in various states as an appendage to the M'Naghten Rule, under which right versus wrong was still considered a vital part of any definition of insanity. In some cases, the Irresistible Impulse Test was considered to be a variation on M'Naghten; in others, it was considered to be a separate test. Though the Irresistible Impulse Test was considered to be an important corrective on M'Naghten's cognitive bias, it still came under some criticism of its own. For example, it seemed to make the definition of insanity too broad, failing to take into account the impossibility of determining which acts were uncontrollable rather than merely uncontrolled, and also making it easier to fake insanity. The test was also criticized for being too narrow; like M'Naghten, the test seemed to exclude all but those totally unable to control their actions. Nevertheless, several states currently use this test along with the M'Naghten Rule to determine insanity, and the American Law Institute in its Model Penal Code definition of insanity adopted a modified version of it.

The Durham Rule

The Durham Rule, a version of which was originally adopted in New Hampshire in 1871, was embraced by the Circuit Court of Appeals for the District of Columbia in the 1954 case of Durham v. United States. The Durham Rule, sometimes referred to as the "product test," provides that the defendant is not "criminally responsible if his unlawful act is the product of a mental disease or defect."

The Durham Rule was originally seen as a way of simplifying the M'Naghten Rule and the Irresistible Impulse Test by making insanity and its relation to the crime a matter of objective diagnosis. Nevertheless, such a diagnosis proved to be more difficult to prove in practice than in theory. The test was criticized because the Circuit Court has provided no real definitions of "product," "mental disease," or "de-fect." Because the Durham Rule proved very difficult to apply, the Circuit Court abandoned it in 1972. Currently, only the state of New Hampshire still uses the Durham Rule as a way to define insanity.

The American Law Institute's Model Penal Code Test

In response to the criticisms of the various tests for the insanity defense, the American Law Institute (ALI) designed a new test for its Model Penal Code in 1962. Under this test, "a person is not responsible for criminal conduct if at the time of such conduct as a result of mental disease or defect he lacks substantial capacity either to appreciate the criminality of his conduct or to conform his conduct to the requirements of the law."

The Model Penal Code test is much broader than the M'Naghten Rule and the Irresistible Impulse Test. It asks whether defendants have a substantial incapacity to appreciate the criminality of their conduct or to conform their conduct to the law rather than the absolute knowledge required by M'Naghten and the absolute inability to control conduct required by the Irresistible Impulse Test.

The ALI test also requires that the mental disease or defect be a mental diagnosis. In this way, it manages to incorporate elements of all three of its predecessors: the knowledge of right and wrong required by M'Naghten, the prerequisite of lack of control in the Irresistible Impulse Test, and the diagnosis of mental disease and defect required by Durham.

Such a broad based rule received wide acceptance, and by 1982 all federal courts and a majority of state courts had adopted the ALI test. While some states have since dropped the ALI test, and it no longer applies at the federal level, 18 states still use the ALI test in their definitions of insanity.

The Hinckley Trial

In 1982, John W. Hinckley, who had attempted in 1981 to assassinate President Ronald Reagan, was acquitted of the crime by a District of Columbia court by reason of insanity. The enormous outrage after Hinckley's acquittal led three states to drop the insanity defense entirely (Montana, Utah, and Idaho, joined by a fourth, Kansas, in 1995). Other states reformed their insanity defense statutes, by adopting the M'Naghten standard over the Model Penal code standard, by shifting the burden of proof from the state to the defense, by changing their commitment and release procedures, or by adopting a "Guilty but Mentally Ill" defense. In addition, the federal courts shifted from the ALI standard to a new law eliminating the Irresistible Impulse Test for insanity defenses in federal crimes.

Current Application of the Insanity Defense

Burden of Proof

The question of who has the burden of proof with an insanity defense has been a source of controversy. Before the Hinckley verdict, a majority of states had the burden of proof rest with the state; that is, the prosecutor had to prove that the defendant was not insane. After the Hinckley verdict, the vast majority of states required the defense to prove that the defendant was indeed insane. In states where the burden is on the defense to prove insanity, the defense is required to show either by 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 are required to prove it beyond a reasonable doubt.

Commitment and Release Procedures

Contrary to uninformed opinion, defendants found not guilty by reason of insanity are not simply released from custody. They are generally committed to mental hospitals where they can be confined for longer than their prison terms would have been. In the case of Jones v. United States, the Supreme Court in 1983 backed this proposition, ruling that the sentence that criminal defendants would have received had they been convicted should have no bearing on how long they could be committed to a mental hospital.

After Hinckley, many states changed their commitment policies to ensure that a defendant found not guilty by reason of insanity would be required to stay in a mental hospital for a certain period of time for evaluation following acquittal. Previously, no time was specified. Also, several states changed the burden of proof for release from the state to defendants.

Distinction Between the Insanity Defense and Competency to Stand Trial

All jurisdictions require that criminal defendants must be competent to stand trial, meaning that defendants understand the nature of the proceedings against them and are able to assist counsel in their defense. A person who is found to be mentally incompetent to stand trial is usually hospitalized for treatment until such time that the person is competent to stand trial. Competency does not address the guilt or innocence of a party, and so competency to stand trial should not be confused with the insanity defense.

The Federal Insanity Defense Reform Act

The federal Insanity Defense Reform Act of 1984, codified at 18 U.S.C. § 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, a response to the Hinckley verdict, 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 defense of insanity 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. The "guilty but mentally ill" verdict allows mentally ill defendants to be found criminally liable and requires them to receive psychiatric treatment while incarcerated, or, alternatively, to be placed in a mental hospital and then, when they are well enough, to be moved to a prison to serve their sentences. Laws allowing pleas and verdicts of guilty but mentally ill were first adopted in Michigan in 1975, and concurrent with or subsequent to the Hinckley trial were adopted by 12 more states.

Status of the Insanity Defense in Criminal Law

Commentators have noted that the insanity defense is risky for criminal defendants because it virtually eliminates any possibility that prosecutors will agree to a plea bargain. Studies, including an eight-state investigation by the National Institute of Mental Health, have shown that the insanity defense is raised in less than one percent of all felony cases. This defense is successful in only a fraction of those cases.

Nevertheless, when the insanity defense is raised, it continues to spur controversy. For instance, in 2001, Andrea Yates of Texas, who allegedly suffered from a mental illness, drown her five children in less than an hour. At her trial for capital murder, Yates' attorneys pleaded the insanity defense, arguing that she suffered post-partum depression. A jury rejected this argument and found her guilty. She received a life sentence for the murders.

The public showed great interest in the Yates trial. Some members of the public, especially but not limited to women's groups, sympathized with Yates due to her battle with post-partum depression. At her trial, four out of five psychiatrists and one psychologist testified that Yates did not know right from wrong. However, the single mental health expert called by the prosecution testified that Yates indeed knew right from wrong, and the jury eventually rejected her insanity defense. Facts later revealed that the state's expert had presented false testimony regarding Yates, and a Texas appellate court in 2005 reversed her conviction and ordered a new trial. Yates v. State, 171 S.W.3d 215 (Tex. App. 2005).

The Yates case demonstrates that in some instances the insanity defense can garner some support. Nevertheless, such a defense is still difficult to prove, and states have not made significant efforts to revise their versions of the insanity defense in recent years.

The Insanity Defense Among the States

Four states, including Kansas, Montana, Idaho, Utah, do not allow the insanity defense. In other states, the standards for proving this defense vary widely. The following provides the status of the insanity defense in each jurisdiction.

ALABAMA: The state uses the M'Naghten Rule. The burden of proof is on the defendant.

ALASKA: The state uses a modified version of the M'Naghten Rule. The burden of proof is on the defendant. A guilty but mentally ill verdict is allowed.

ARIZONA: The state uses a modified version of the M'Naghten Rule. The burden of proof is on the defendant. A guilty but insane verdict is allowed.

ARKANSAS: The state uses a modified version of the Model Penal Code rule. The burden of proof is on the defendant.

CALIFORNIA: The state uses the M'Naghten Rule. The burden of proof is on the defendant.

COLORADO: The state uses a modified version of the M'Naghten Rule with the Irresistible Impulse Test. The burden of proof is on the state.

CONNECTICUT: The state uses a modified version of the Model Penal Code rule. The burden of proof is on the defendant.

DELAWARE: The state uses a modified version of the Model Penal Code rule. The burden of proof is on the defendant.

DISTRICT OF COLUMBIA: The state uses the Model Penal Code rule. The burden of proof is on the defendant.

FLORIDA: The state uses the M'Naghten Rule. The burden of proof is on the state.

GEORGIA: The state uses a modified version of the M'Naghten Rule. The burden of proof is on the defendant. A guilty but mentally ill verdict is allowed.

HAWAII: The state uses the Model Penal Code rule. The burden of proof is on the defendant.

IDAHO: The state has abolished the insanity defense. The state allows a guilty but insane verdict.

ILLINOIS: The state uses a modified version of the Model Penal Code rule. The burden of proof is on the defendant.

INDIANA: The state uses a modified version of the Model Penal Code rule. The burden of proof is on the defendant.

IOWA: The state uses the M'Naghten Rule. The burden of proof is on the defendant.

KANSAS: The state has abolished the insanity defense.

KENTUCKY: The state uses the Model Penal Code rule. The burden of proof is on the defendant.

LOUISIANA: The state uses the M'Naghten Rule. The burden of proof is on the defendant.

MAINE: The state uses a modified version of the Model Penal Code rule. The burden of proof is on the defendant.

MARYLAND: The state uses the Model Penal Code rule. The burden of proof is on the defendant.

MASSACHUSETTS: The state uses the Model Penal Code rule. The burden of proof is on the state.

MICHIGAN: The state uses the Model Penal Code rule. The burden of proof is on the state.

MINNESOTA: The state uses the M'Naghten Rule. The burden of proof is on the defendant.

MISSISSIPPI: The state uses the M'Naghten Rule. The burden of proof is on the state. An acquitted by reason of insanity verdict is allowed.

MISSOURI: The state uses a modified version of the M'Naghten Rule. The burden of proof is on the defendant.

MONTANA: The state has abolished the insanity defense, although a guilty but insane verdict is allowed.

NEBRASKA: The state uses the M'Naghten Rule. The burden of proof is on the defendant.

NEVADA: The state uses the M'Naghten Rule. The burden of proof is on the defendant.

NEW HAMPSHIRE: The state uses the Durham standard. The burden of proof is on the defendant.

NEW JERSEY: The state uses the M'Naghten Rule. The burden of proof is on the state.

NEW MEXICO: The state uses the M'Naghten Rule with the Irresistible Impulse Test. The burden of proof is on the state.

NEW YORK: The state uses the Model Penal Code rule. The burden of proof is on the defendant.

NORTH CAROLINA: The state uses the M'Naghten Rule. The burden of proof is on the defendant.

NORTH DAKOTA: The state uses the Model Penal Code rule. The burden of proof is on the state.

OHIO: The state uses the M'Naghten Rule. The burden of proof is on the defendant.

OKLAHOMA: The state uses the M'Naghten Rule. The burden of proof is on the state.

OREGON: The state uses the Model Penal Code rule. The burden of proof is on the defendant.

PENNSYLVANIA: The state uses the M'Naghten Rule. The burden of proof is on the defendant.

RHODE ISLAND: The state uses the Model Penal Code rule. The burden of proof is on the defendant.

SOUTH CAROLINA: The state uses the M'Naghten Rule. The burden of proof is on the defendant.

SOUTH DAKOTA: The state uses the M'Naghten Rule. The burden of proof is on the defendant.

TENNESSEE: The state uses the Model Penal Code rule. The burden of proof is on the state.

TEXAS: The state uses the M'Naghten Rule with the Irresistible Impulse Test. The burden of proof is on the defendant.

UTAH: The state has abolished the insanity defense, but guilty but mentally ill verdicts are allowed.

VERMONT: The state uses the Model Penal Code rule. The burden of proof is on the defendant.

VIRGINIA: The state uses the M'Naghten Rule with the Irresistible Impulse Test. The burden of proof is on the defendant.

WASHINGTON: The state uses the M'Naghten Rule. The burden of proof is on the defendant.

WEST VIRGINIA: The state uses the Model Penal Code rule. The burden of proof is on the state.

WISCONSIN: The state uses the Model Penal Code rule. The burden of proof is on the defendant.

WYOMING: The state uses the Model Penal Code rule. The burden of proof is on the defendant.

Additional Resources

American Jurisprudence. 2d Edition. Thomson/West 2005.

Mental Health and Disability Law in a Nutshell. Donald H.J. Hermann, West Group, 1997.

Toward a New Test for the Insanity Defense: Incorporating the Discoveries of Neuroscience into Moral and Legal Theories. Reider, Laura, UCLA Law Review, Oct. 1998.


American Bar Association Criminal Justice Section

740 15th Street, NW, 10th Floor
Washington, DC 20005-1009 USA
Phone: (202) 662-1500
Fax: (202) 662-1501

American Psychological Association (APA)

750 First Street, NE
Washington, DC 20002-4242 USA
Phone: (202) 336-5510

Association of Federal Defense Attorneys

8530 Wilshire Blvd., Suite 404
Beverly Hills, CA 90211 USA
Phone: (310) 397-1001

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Insanity defense

A defense in which a person can be found not guilty, or not responsible, for a crime because, at the time of the crime, the accused was unable to differentiate between right and wrong, based on the fact that the accused suffers from mental illness or mental defect.

The insanity defense allows a mentally ill person to avoid being imprisoned for a crime on the assumption that he or she was not capable of distinguishing right from wrong. Often, the sentence will substitute psychiatric treatment in place of jail time. The idea that some people with mental illness should not be held responsible for crimes they commit dates back to the Roman Empire, if not earlier. The "not guilty by reason of insanity" (NGRI) verdict rests in part on two assumptions: that some mentally ill people cannot be deterred by the threat of punishment , and that treatment for the defendant is more likely to protect society than a jail term without treatment.

It is important to note that "insanity" is a legal term, not a psychological one, and experts disagree whether it has valid psychological meaning. Critics of NGRI have claimed that too many sane defendants use NGRI to escape justice; that the state of psychological knowledge encourages expensive "dueling expert" contests that juries are unlikely to understand; and that, in practice, the defense unfairly excludes some defendants. Research on NGRI fails to support most of these claims; but some serious problems may exist with NGRI.

Insanity defense statistics

One problem with discussing NGRI is that there are, strictly speaking, 51 types of insanity defense in the United Statesone for each set of state laws, and one for federal law. Some states allow an NGRI defense either when defendants lack awareness that what they did was wrong (called mens rea, or literally "guilty mind") or lack the ability to resist committing the crime (actus rea, "guilty act"), while other states only recognize mens rea defenses.

Successful NGRI defenses are rare. While rates vary from state to state, on average less than one defendant in 1000.85 percent actually raises the insanity defense nationwide. Interestingly, states with higher rates of NGRI defenses tend to have lower success rates for NGRI defenses; the percentage of all defendants found NGRI is fairly constant, at around 0.26 percent.

In some studies, as many as 70 percent of NGRI defendants withdrew their plea when a state-appointed expert found them to be legally sane. In most of the rest, the state didn't contest the NGRI claim, the defendant was declared incompetent to stand trial, or charges were dropped. High-profile NGRI cases involving rich defendants with teams of experts may grab headlines and inflame the debate, but they are very rare.

Problems with NGRI

Some problems, however, have emerged with NGRI. Regulation concerning who can testify as to the sanity of a defendant is very inconsistent from state to state. According to one national survey, only about 60 percent of states required an expert witness in NGRI determinations be a psychiatrist or psychologist; less than 20 percent required additional certification of some sort; and only 12 percent required a test. So the quality of expert witnesses may vary from state to state.

The quality of post-NGRI psychiatric treatment may be another problem. Treatment varies from state to state in both duration and, some say, quality; some defendants spend more time in mental institutions than they would have spent in jail had they been convicted, some less. NGRI defendants tend to spend more time in institutions than patients with similar diagnoses who were not accused of a crime, which undercuts somewhat the argument that treatment, not punishment, is the goal.

In terms of preventing repeat offenses, psychiatric treatment seems to help. Some studies suggest high posttreatment arrest rates, but these arrests tended to be for less serious crimes. At least one study indicated that average time to arrest of these patients after release is no higher than for the general population.

Mock jury studies indicate that jurors do carefully consider and discuss many factors in an insanity defense, but may be ignoring the local legal definitions of insanity. Mock juries tended to render the most NGRI verdicts when the defendant showed a lack of both ability to understand and ability to resist committing the crime, even though no state requires both and some consider ability to resist to be irrelevant. In addition, personal feelings about the legitimacy of the insanity defense may influence jurors' decisions.

One of the most devastating arguments against NGRI is that it may unfairly exclude many defendants. Studies suggest high rates of psychiatric illness in the general prison population. Many mentally ill defendants never get a chance to plead NGRI; some obviously psychotic defendants fight to prevent their attorneys from mounting an insanity defense for them.

The unwillingness of many states to accept an actus rea defense bothers some experts. Biochemical studies indicate that some people have biochemical abnormalities that may make them unable to control their impulses. If this is true, these people cannot voluntarily conform to the law, and therefore they have grounds for NGRI. On the other hand, a huge proportion of the prison population may suffer from varying degrees of such a mental defectand finding them all NGRI would probably be dangerous to society as well as not viable.

Guilty but mentally ill

As an alternative to NGRI, some states have added a third possible verdict to the usual trio of guilty, not guilty, and NGRIthe verdict of "guilty but mentally ill" (GBMI). In theory, this recognizes when a defendant's mental illness played an important role in a crime without entirely causing it. The state incarcerates the defendant for the crime, but also treats him or her for the mental illness.

Unfortunately, states with GBMI verdicts have sometimes neglected to provide for treatment; therefore many of these defendants are jailed without treatment, exactly as if they had been found guilty. Another dilemma with the GBMI verdict may be an "easy out" for jurors. If a jury finds the defendant guilty, they may not spend time worrying about whether he or she may be sane; because they find the defendant mentally ill, they may not address the fact that the defendant should actually be found NGRI. Hence, the insanity defense "problem" will not yield to easy solutions.

Kenneth B. Chiacchia

Further Reading

Berman, Mitchell E. and Emil F. Coccaro. "Neurobiologic correlates to violence: relevance to criminal responsibility." Behavioral Sciences and the Law 16: 303-318 (1998).

Brewer, Steve and John Makeig. "Mental hospital loses trust of legal system." Houston Chronicle (Nov. 15, 1999): A, 1:5.

Caplan, Lincoln. "Annals of law: the insanity defense." The New Yorker (July 2, 1984): 45-78.

Lymburner, Jocelyn A. and Ronald Roesch. "The insanity defense: five years of research (1993-1997). " International Journal of Law and Psychiatry 22(3-4): 213-240 (1999).

"Real help for inmates." Denver Post (Nov. 14, 1999): G4:1.

Shroeder, William A. "Time to abolish the insanity defense." St. Louis Post-Dispatch (Jan. 26, 2000): C.13.

Tolson, Mike. "Is mentally ill death row inmate sane enough to die?" Houston Chronicle (Nov. 14, 1999): A, 1:1.

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Insanity Defense

A defense asserted by an accused in a criminal prosecution to avoid liability for the commission of a crime because, at the time of the crime, the person did not appreciate the nature or quality or wrongfulness of the acts.

Clark v. Arizona

There are no constitutional precedents regarding the use of the insanity defense in criminal trials, and since its inception in 18th century British common law, courts have left the consideration of a defendant's mental state to the courts and triers of fact. In the highly anticipated case of Clark v. Arizona, No. 05-5966, the U.S. Supreme Court upheld the State of Arizona's limited use of insanity evidence solely for the purpose of determining an ability to distinguish right from wrong. The Court found that this limitation did not violate a defendant's due process rights under the Fifth and Fourteenth Amendments to the U.S. Constitution.

The Court also found no violation in Arizona's restricted use of defense evidence of mental illness or incapacity solely for the purpose of proving an affirmative defense of insanity. In the present case, Arizona's narrow use of such evidence eliminated defendant Clark's ability to use evidence of his mental illness to counter prosecution's proof of mens rea, or the mental element of criminal intent, needed to establish the crime of first degree murder.

The background facts showed that in the early morning hours of June 21, 2000, Officer Jeffrey Moritz of the Flagstaff, Arizona police responded in uniform to complaints that a pickup truck with blaring music was circling a residential block. When Officer Moritz spotted the truck, he turned on his emergency lights and siren on his marked patrol car. Seventeen-year-old Eric Clark pulled over. Officer Moritz got out of the patrol car and told Clark to stay where he was, but Clark shot the officer and ran away on foot. Officer Moritz was able to call for backup help before he died. Later that day, Clark was arrested with gunpowder residue still on his hands. A gun later traced to the one that killed the officer was found nearby, stuffed inside a knit cap.

Clark was charged with first-degree murder under Ariz. Rev. Stat. Ann. §§13-1105(A)(3), intentionally or knowingly killing a law enforcement officer in the line of duty. Clark waived his right to a jury and the case was heard by the state court.

At trial, Clark did not contest the shooting and death, but focused on his mental state. The defense tried to use evidence of Clark's undisputed paranoid schizophrenia in two contexts. First, it was introduced to support an affirmative defense of insanity. Second, it was used in an attempt to rebut evidence of the requisite criminal intent. Defense argued that Clark's mental illness at the time of the incident prevented him from having the specific intent to "intentionally and knowingly" kill a law enforcement officer.

Following this, prosecution rebutted with circumstantial evidence showing Clark's knowledge that Officer Moritz was a police officer, e.g., that Clark acknowledged the symbols of police authority and stopped and pulled over when Moritz sounded his sirens and activated his emergency lights behind Clark. Other testimony was offered which tended to show that Clark had intentionally lured a police officer to the area in order to kill him, having told several people a few weeks earlier that he wanted to shoot police officers.

The trial court refused to consider defense evidence bearing on the issue of mental illness for purposes of rebutting the element of mens rea. The court cited State v. Mott, 187 Ariz. 536, cert. denied, 520 U.S. 1234 (1997), in which that court refused to allow psychiatric testimony to negate specific intent, and held that "Arizona does not allow evidence of a defendant's mental disorder short of insanity … to negate the mens rea element of a crime." 187 Ariz. at 541.

At the close of Clark's trial, the judge issued a special verdict of first degree murder, expressly finding that Clark had shot and killed Officer Moritz beyond a reasonable doubt, and that Clark had failed to show that he was insane at the time. The judge further expressly noted that any mental illness from which Clark suffered did not distort his perception of reality so severely that he did not know his actions were wrong. Clark was sentenced to life imprisonment.

Clark moved to vacate the judgment and sentence, mainly arguing that Arizona's insanity test and its Mott rule each violated due process. The cou rt denied the motion. The Court of Appeals of Arizona affirmed. The Supreme Court of Arizona denied further review, and the U.S. Supreme Court granted certiorari on the question of whether due process prohibited Arizona from narrowing its insanity test or excluding evidence of mental illness/incapacity to rebut evidence of criminal intent.

Justice Souter delivered the majority opinion of a divided Court. He was joined by Chief Justice Roberts and Justices Scalia, Thomas, and Alito. Justice Breyer concurred in part and in the ultimate disposition, but filed a separate opinion also dissenting in part. Justices Kennedy, Stevens, and Ginsburg dissented.

The Court discredited Clark's argument that Arizona's departure from the landmark English case that provided the foundation for considering mental state (McNaghten's Case, 1843) offended a basic principle of justice "so rooted in the traditions and conscience of our people as to be ranked as fundamental," (quoting Patterson v. New York, 432 U.S. 197). Neither did Arizona's abbreviated version of the McNaghten statement raise any claim that some constitutional minimum had been shortchanged. Cognitive incapacity is relevant under both the abbreviated and full statement, and evidence going to cognitive incapacity has the same significance under both.

Likewise, said the Court, the Arizona Supreme Court's Mott rule does not violate due process, and the reasons supporting the rule satisfy due process. They include Arizona's authority to define its presumption of sanity by choosing an insanity definition and placing the burden of persuasion on criminal defendants claiming incapacity as an excuse. Arizona's rule also serves to avoid juror confusion or misunderstanding.

The dissent argued that Clark should have been permitted to introduce "critical and reliable" evidence showing that he lacked intent or knowledge.