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Position Statement 57: In Support of the Insanity Defense


Society has long recognized the need to distinguish between those defendants charged with a crime who are and those who are not responsible for their acts.[1][2] The insanity defense exists to identify which individuals fall into the latter category because of a mental disability. When the nature of defendants’ mental impairments are such that they are not criminally responsible for their acts, it is not only unjust to impose criminal liability and punishment, but it is also ineffective.[2] Therefore, the Mental Health America’s position is as follows:

  • It is vital that states provide for the ongoing availability of a complete insanity defense resulting in a verdict of not guilty by reason of insanity.
  • When the insanity defense does not apply, the availability of mens rea and diminished capacity defenses remains critically important.
  • “Guilty but mentally ill” laws should be abolished as they are ineffective, unjust and misleading.
  • States must provide individuals who are acquitted by reason of insanity with appropriate, recovery-based treatment, rather than treat these defendants as if they have been found guilty.
  • The decision whether to plead insanity must be entirely the defendant’s, although courts should take action to ensure that the defendant is capable of understanding the consequences of the decision.

The Insanity Defense

Criminal sanctions promote public safety through the deterrent effect of the punishment itself and through the stigma of a criminal conviction. Criminal sanctions also further retributivist goals. Without blameworthiness, however, punishment is not justified.[1] When an individual is determined to be not criminally responsible, acquittal via a verdict of “not guilty by reason of insanity” (NGRI) is the only appropriate action. Since concerns about public safety and the need for treatment usually remain after acquittal, these concerns should be addressed through involuntary treatment in mental hospitals rather than through confinement in prison.

Necessary Components of a Comprehensive Insanity Defense

In order to effectively distinguish between those who are and those who are not criminally responsible for their acts, the insanity defense must contain both a “cognitive” prong and a “volitional” prong.[3] That is, an insanity defense should exculpate both those who are unable to understand that their act is wrong, as well as those who are unable, due to mental disability, to control their actions.

Section 4.01 of the Model Penal Code (MPC), promulgated by the American Law Institute (ALI),[4] provides a comprehensive insanity defense. Section 4.01 of the MPC remains substantially unchanged from when it was initially drafted in 1962 and currently provides as follows:

Section 4.01: Mental Disease or Defect Excluding Responsibility.

(1) A person is not responsible for criminal conduct if at the time of such conduct as a result of mental disease or defect he [or she] lacks substantial capacity either to appreciate the criminality/wrongfulness of his [or her] conduct or to conform his [or her] conduct to the requirements of the law.

(2) As used in this Article, the terms “mental disease or defect” do not include an abnormality manifested only by repeated criminal or otherwise anti-social conduct.

This formulation represents the consensus of American legal scholars on the appropriate scope of the insanity defense.[3] § 4.01(1) establishes both “cognitive” and “volitional” prongs, ensuring that the defense is appropriately inclusive, but § 4.02(2) minimizes the risk that the defense will be over inclusive or actually encourage repeated criminal activity.[5] Mental Health America (MHA) endorses the MPC formulation of the insanity defense.

The Insanity Defense in Practice

Despite public fears, defendants do not abuse the availability of the insanity defense. In felony cases, the defense is invoked less than 1% of the time, and even when it is employed, it is only successful 25% of the time.[6] Further, in approximately 70% of the cases in which the defense has been successfully employed, the prosecution and defense have agreed on the appropriateness of the insanity plea before the trial.[6] That individual invocations of the defense are contested relatively infrequently suggests that it is no more likely for a defendant to be incorrectly found not guilty by reason of insanity than to be incorrectly found not guilty for any other reason. Finally, there is a high likelihood of court-mandated treatment following an insanity acquittal, often lasting a substantial length of time, which serves protect the public from defendants who may be dangerous and also to discourage people from pretending to be mentally ill in order to use the defense.[7] These realities all refute perceptions that the insanity defense creates a loophole in criminal liability.

Although the wariness with which the public often views the insanity defense is unmerited, some states’ insanity laws nonetheless reflect this suspicion. After the MPC was first promulgated, most states initially incorporated identical or substantially similar defenses into their laws. Since the late 1970s, however, many states have taken action to limit their insanity defense laws and to bring them back toward pre-MPC formulations.[8] As of 2004, only 20 states still had insanity defense laws that incorporated the MPC formulation in its entirety or in a substantially similar fashion.[9] As of 2010, four states (Idaho, Kansas, Montana, Utah) had eliminated the insanity defense entirely,[10] and the remainder have limited the insanity defense to the cognitive prong.[9]

The two-pronged protection of § 4.01 is necessary in order to comply with two different constitutional requirements: due process and the prohibition against cruel and unusual punishment.[11] In considering these issues, however, the Supreme Court has left considerable discretion to state courts. The Court has indicated that states may be required to provide at least some minimal defense based on mental illness, but has not yet found a state’s law to be below that minimum and has declined to specify exactly what that minimum entails. The court upheld Arizona’s limited insanity defense in Clark v. Arizona,[12] and denied certiorari in Delling v. Idaho,[13] a case alleging that Idaho’s replacement of the insanity defense with a “guilty but mentally ill” verdict constitutes a due process violation. Still, three justices dissented from the Court’s denial of certiorari in Delling, arguing that Idaho’s practice does violate the constitution. MHA agrees with this dissenting position.

MHA strongly opposes the popular, scientifically-unfounded belief that mental illness predisposes a person to act violently. See MHA Position Statement 72, Violence: Community Mental Health Response, Thus, restricting the insanity defense would not enhance public safety.

The Mens Rea and Diminished Capacity Defenses

To be guilty of a crime, a person must intend to do the act that the state seeks to punish. This “mens rea” is a constitutional requirement, although courts have allowed states to limit it in certain ways. Thus far, the Supreme Court has held that a diminished capacity defense is not constitutionally guaranteed. But Mental Health America believes that people accused of crimes should be able to assert mens rea and diminished capacity defenses at trial using expert psychological evidence.

Defining the Defenses

In anything more than trivial offenses, a finding of guilt in a criminal trial generally requires some form of mens rea, or “guilty mind,” often expressed as knowledge or intent.[14] A defendant that does not have the required mens rea is not guilty of the crime.[15] This is the mens rea defense.

A diminished capacity defense is different from a mens rea defense, but the two overlap considerably and there is not always a clear distinction between the two. A diminished capacity defense allows for mitigation of a criminal conviction based on the defendant’s mental impairment, even if the insanity and mens rea defenses have both failed.[16] The diminished capacity defense reflects the notion that a defendant, while guilty, may, nevertheless, be guilty of a less serious crime due to  mental impairment.

The Defenses in Practice

A crime’s required mens rea is a critical element of the offense, and without it a defendant cannot be found guilty.[15] However, some courts have upheld state laws that interfere with this requirement. The Supreme Court in Clark upheld Arizona’s rule that effectively precludes the use of most psychological evidence in making a mens rea or diminished capacity defense at trial, and instead relegated it to use only in pleading insanity.[17] In so holding, the Court simultaneously limited the defendant’s ability to establish a mens rea defense and declared that diminished capacity defenses are not constitutionally required. As of 2007, only three states still allowed a diminished capacity defense.[18]

As the dissent in that case noted, the practical effect of this rule is that “a person would be guilty of first-degree murder if he knowingly or intentionally …committed the killing under circumstances that would show knowledge or intent but for the defendant’s mental illness.”[19] MHA joins this dissent in arguing that such a rule is unconstitutional because it results in a guilty verdict even when the defendant did not satisfy a critical element of the crime. Moreover, even if the defendant possessed the required mens rea, the mental illness may remain relevant to determining the extent of his or her blameworthiness, thus necessitating a diminished capacity defense as well.

The MPC Approach

The MPC both assures a mens rea defense and establishes a limited diminished capacity defense in the same section, which provides as follows:

Section 4.02: Evidence of Mental Disease or Defect Admissible When Relevant to Element of the Offense; Mental Disease or Defect Impairing Capacity as Ground for Mitigation of Punishment in Capital Cases.

(1) Evidence that the defendant suffered from a mental disease or defect is admissible whenever it is relevant to prove that the defendant did or did not have a state of mind that is an element of the defense.

(2) Whenever the jury or the Court is authorized to determine or to recommend whether or not the defendant shall be sentenced to death or imprisonment upon conviction, evidence that the capacity of the defendant to appreciate the criminality [wrongfulness] of his [or her] conduct or to conform his [or her] conduct to the requirements of law was impaired as a result of mental disease or defect is admissible in favor of a sentence of imprisonment.

Viewed in light of § 4.01, § 4.02 indicates that mens rea and diminished capacity defenses are to be available independently of the insanity defense. § 4.02(2) provides a diminished capacity defense only in capital cases. While this formulation is more protective than the current law in the vast majority of states, the diminished capacity defense should not be limited to capital cases. A broader, but still sufficiently limited, defense would allow diminished capacity mitigation in all specific intent crimes, not only in capital crimes.

Guilty but Mentally Ill Laws

Laws establishing a “guilty but mentally ill” (GBMI) verdict are inappropriate for two reasons. First, they are inappropriate because the GBMI verdict is no different in practice from a finding of guilty. Second, they are inappropriate because this alternative to the insanity defense may confuse jurors. These fundamental problems persist whether the GBMI verdict is provided in addition to, or as a replacement for, the NGRI verdict.

A GBMI verdict provides no benefit to society or to criminal defendants because it has the same consequences as a guilty verdict.  Someone found GBMI may be given any sentence that she or he could have been given if found guilty.  That includes a sentence of death.[20]  Virtually every person found GBMI is sent to prison.   Persons found GBMI are entitled to mental health services while imprisoned.  However, they have no greater right to mental health services in prison than those simply found guilty.  That is because all persons confined in prison have a constitutional right to mental health services.[21] While GBMI statutes typical permit defendants to be transferred to mental hospitals, these provisions are permissive rather than mandatory and are rarely utilized.[22]

Because the GBMI verdict is indistinguishable from the guilty verdict, GBMI laws serve no purpose other than to confuse jurors. Jurors may understandably believe that the GBMI verdict is a compromise between the NGRI and guilty verdicts, and thus the availability of a GBMI verdict may cause them to find a defendant GBMI when they would not have been willing to give a guilty verdict. This issue is compounded by the fact that jurors are often wary of the NGRI verdict. [23] Although empirical evidence from actual trials is not yet available, researchers have considered, in the mock trial setting, the impact on jury preferences of the simultaneous availability of NGRI and GBMI verdicts.[24] Research indicates that juries may use GBMI as a mechanism for “avoiding the difficult moral and social issues raised by an insanity defense.”[24]

Defendants’ challenges of the GBMI verdict as a due process violation have yet to succeed.[25] As of 2009, over 20 states provided for a GBMI verdict.[26]  Four of these states had eliminated the NGRI verdict entirely and replaced it with GBMI.[10] The remaining 16 states with GBMI laws allow for both an NGRI verdict and a GBMI verdict.  In either context, the GBMI verdict is inappropriate and seriously undermines the important policies that require maintaining the insanity and diminished capacity defenses, discussed above.

The Consequences of Pleading Insanity

An individual who is acquitted on the basis of insanity should be treated. However, it is critically important, both out of concern for promoting the public safety and out of concern for the defendant’s rights, that the purpose of this treatment is rehabilitation, not to serve as a punitive alternative to imprisonment. That is, the aim of the treatment should be to eventually release an individual into the community, not to punish that individual for a crime for which the defendant has been judged not morally culpable.

In Jones v. US, the Supreme Court found it constitutional for states to confine insanity acquittees in a mental health facility for periods longer than they would have been imprisoned had they been found guilty of the crime.[27] In reality, this routinely occurs.[28] This practice is appropriate only for as long as the additional period of confinement is clinically justified and serves a valuable rehabilitative purpose. It is critical that insanity acquittees are released when they are no longer dangerous to society.

Allowing these extended treatment periods may very well further legitimate goals, but the policy of long-term treatment after NGRI verdicts increases the risk of treatment being used as a pretext for punishment. In order to protect against this, states should adopt rigorous standards and procedures.. Review boards that are as independent of the criminal justice system and of the courts as possible are one mechanism to achieve this goal. These boards serve to monitor an insanity acquittee’s clinical progress and evaluate the need for continued treatment on an ongoing basis. The modern trend in states with a full insanity defense is toward use of such a system.[29] Independent review boards serve to place the treatment and release decision-making process in the hands of those most qualified to make such determinations, and those who are most likely to act only out of public safety and treatment concerns.

The Decision to Plead Insanity

People found not guilty by reason of insanity will often be confined longer than they would have been had they been found guilty.[30]  The conditions of their confinement will also be quite restrictive.  Of course, it is true that in most jurisdictions most persons with serious mental illnesses will be safer and receive better care in a mental hospital than in a prison.  But respect for individual autonomy requires that the defendant be permitted to choose between these two difficult outcomes.  It is critical that the decision to plead insanity is left to the defendant.

However, precisely because the decision whether to plead insanity is difficult, it is important that courts insure that criminal defendants have the capacity to make this choice and are provided with all of the relevant information. The likely length of confinement after an NGRI verdict and the likely treatment to be received are critical factors in deciding whether or not to invoke the insanity defense.  And these consequences may be difficult to predict. Just as courts must ensure that defendants are competent to plead guilty and are aware of the consequences, so too should courts ensure that defendants are competent to plead insanity and are informed about the likely consequences of the plea.[31]

Call to Action

MHA encourages policy and legal changes as necessary in order to achieve the following goals:

  • States should provide a full insanity defense. When defendants’ mental illnesses prevent them from understanding the wrongfulness of the act or prevent them from controlling their behavior, they should be acquitted by reason of insanity. Criminal liability in these instances is neither appropriate nor effective.
  • Even if a defendant does not qualify for an insanity acquittal, the mental illness may remain critically relevant to the criminal proceedings. States should therefore also provide for separate, albeit related, mens rea and diminished capacity defenses. 
  • “Guilty but mentally ill” verdicts are ineffective and unjust.  States should neither replace the insanity defense with this disposition nor offer it as an alternative to judges and jurors considering an insanity defense.
  • People acquitted because of a finding of  insanity should be treated in an appropriate clinical setting. The purpose of this treatment should be rehabilitative, not punitive.
  • Because of the weighty implications of the decision to plead insanity, the defendant must be the one to decide whether to use the insanity defense.  However, courts should act to ensure that the defendant is capable of understanding the consequences of the decision. Until a defendant can do so, the state should not find him or her fit to stand trial.

Effective Period

The Mental Health America Board of Directors approved this policy on June 8, 2014. It will remain in effect for five (5) years and is reviewed as required by the Mental Health America Public Policy Committee.

Expiration: December 31, 2019


[1] Livermore, Joseph and Paul Meehl. The Virtues of M’Naghten. Minnesota Law Review. Vol. 51. 789: 790-793 (1966).

[2] Winkel, Susan. Free Fill, Responsibility & Forensic Psychiatry: An Exploration of Justifications for the Insanity Defense. GGzet Wetenschappelijk, Vol. 17, No. 1: 36, 44 (2013).

[3] Bonnie, Richard. The Moral Basis of the Insanity Defense. American Bar Association Journal. Vol. 69, No. 2: 794, 795 (1983).

[4] About the American Law Institute. American Law Institute. Available at (Last visited Feb. 15, 2014).

[5] Robinson, Paul. An Overview of Mental Illness Under U.S. Criminal Law. University of Pennsylvania Law School, Public Research Paper, 2 (2013).

[6] Costanzo, Mike and Daniel Krauss. Forensic and Legal Psychology. Worth Publishers, 206 (2012).

[7] Braff, Jeraldine, et al. Detention Patterns of Successful and Unsuccessful Insanity Defendants. Criminology, Vol. 21, No. 3: 439, 446 (1983).

[8] Robinson, Paul and Markus Dubber. An Introduction to the Model Penal Code. University of Pennsylvania Law School, 15. Available at (Last visited Feb. 15, 2014).

[9] State Court Organization, The Defense of Insanity: Standards and Procedures. Department of Justice. Table 35, 209-212 (2004). Available at (Last visited Feb. 15, 2014).

[10] Lillienfeld, Scott and Hal Arkowitz. The Insanity Verdict on Trial. Scientific American, Dec. 23, 2010. Available at (Last visited Feb. 21, 2014).

[11] Robitscher, Jonas and Andrew Haynes. In Defense of the Insanity Defense. Emory Law Review, Vol. 31: 9, 59 (1982).

[12] See Clark v. Arizona, 548 U.S. 735, 755 (2006).

[13] See Delling v. Idaho, 133 S.Ct 504, 504 (2012).

[14] Arenella, Peter. The Diminished Capacity and Diminished Responsibility Defenses: Two Children of a Doomed Marriage. Columbia Law Review, Vol. 77, No. 6: 827, 829 (1977).

[15] Parry, John and Eric Drogin. Mental Disability Law, Evidence, and Testimony. American Bar Association, 207 (2007).

[16] Id. at 208.

[17] Clark v. Arizona, 548 U.S. 779.

[18] Parry at 209.

[19] Clark v. Arizona, 548 U.S. 797 (Kennedy, J., dissenting) (emphasis added).

[20]See People v. Crews, 122 Ill.2d 266, 294 (1988); State v. Anderson, 966 So.2d 973, 984 (2008).

[21]  See Estelle v. Gamble, 97 S.Ct 285, 291 (1976)(holding that deliberate indifference to prisoner’s serious medical needs constitutes a violation of the 8th Amendment’s prohibition again cruel and unusual punishment). See also Brown v. Plata, 131 S.Ct 1910, 1947 (2011)(Reaffirming that the 8th Amendment requires the state to provide medical treatment, specifically mental health treatment, to prisoners).

[22] See, e.g., 730 ILCS 5/5-2-6.

[23]Smith, Steven. Neuroscience, Ethics, and Legal Responsibility: The Problem of the Insanity Defense. Springer. Journal of Science and Engineering Ethics, Vol 18: 475, 478 (2012).

[24 ]Melville, John and David Naimark. Punishing the Insane: The Verdict of Guilty but Mentally Ill. American Academy of Psychiatry Law Journal, Vol. 30: 553, 553 (2002).

[25] See, e.g., People v. Lantz, 186 Ill.2d 243, 255 (Reversing an appellate court decision that held that Illinois’s GBMI law violates due process).

[26] Kutys, Jennifer and Jennifer Esterman. Guilty but Mentally Ill (GBMI) vs. Not Guilty by Reason of Insanity (NGRI): An Annotated Bibliography. The American Society of Trial Consultants. The Jury Expert, 28. Available at (Last visited Feb. 19, 2014).

[27] See Jones v. US, 463 U.S. 354, 370 (1983).

[28] Silver, Eric. Demythologizing Inaccurate Perceptions of the Insanity Defense. American Psychiatric Association Journals, Law and Human Behavior, Vol. 18, No. 1: 63, 63 (1994).

[29] Hafemeister, Thomas and John Petrila. Treating the Mentally Disordered Offender: Society’s Uncertain, Conflicted, and Changing Views. Florida State University Law Review, Vol. 21: 729, 749-750 (1993); Shaefer, Michele and Joseph Bloom. The Use of the Insanity Defense as a Jail Diversion Mechanism for Mentally Ill Persons Charged with Misdemeanors. American Academy of Psychiatry Law Journal, Vol. 33: 79, 81 (2005).

[30] Ellis, James. The Consequences of the Insanity Defense: Proposals to Reform Post-Acquittal Commitment Laws. Catholic University Law Review, Vol. 35: 961, 1019 (1986).

[31] Reisner, Andrew, et al. Competency to Stand Trial and Defendants Who Lack Insight Into Their Mental Illness. American Academy Psychiatry Law Journal, Vol. 41: 85, 86 (2013).


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