Dia Shrivastava

May 16, 2026

Introduction

When should mentally ill defendants be held criminally responsible and when should the insanity defense excuse liability? 

The insanity defense reflects the tension between psychological science and legal standards of responsibility [8,11]. However, its rarity and strict requirements show that mentally ill defendants are not exempt from justice; rather, the legal system holds them accountable in a different way when severe mental illness prevents true criminal responsibility [5,6]. While severe mental illnesses can impair an individual’s ability to understand or control their actions, the legal system has strict criteria in place to determine their criminal responsibility [6,8]. Many people believe that the insanity defense allows defendants to escape punishment. However, according to Mental Health America, the insanity defense is used in less than one percent of felony cases and succeeds only about twenty-five percent of the time [5]. Even when successful, it typically results in long-term confinement in secure psychiatric institutions rather than freedom [5,6]. For that reason, the insanity defense should be understood not as a loophole, but as a limited legal safeguard for defendants whose severe mental illness prevents true criminal responsibility.

Legal Definition of Insanity

The insanity defense is a legal argument used in criminal cases where the defendant admits that they committed the act, but claims they should not be held legally responsible due to a mental condition that prevented them from understanding what they were doing or recognizing that their actions were wrong [6]. Therefore, the insanity defense does not question whether the defendant committed the act, but whether their mental state at the time absolves them of responsibility [6]. For example, in United States v. Hinckley (1982), Hinckley, the defendant, did not deny the shooting itself; instead, the case centered on whether his mental illness prevented criminal responsibility [10]. If the insanity defense is successful, the defendant is typically found not guilty by reason of insanity, meaning they are not considered criminally responsible due to their psychological state at the time of the offense [6].

In criminal law, responsibility usually requires mens rea, an awareness of one’s actions, and understanding right from wrong [6]. Mens rea refers to the guilty mind, meaning the person must have the mental intent necessary for criminal responsibility [6]. The insanity defense argues that mental illness prevents the accused from meeting these factors and legal requirements, therefore the individual cannot be held criminally responsible [6,8]. However, this does not mean that the defendant is released entirely, but instead is committed to a secure mental health facility under court supervision to receive proper treatment and ensure public safety, and in some cases, that confinement may last longer than a typical prison sentence [5,6]. This treatment is generally viewed as a more humane and empathetic response, given the individual’s mental condition [11].

There are four main legal tests used to determine insanity [8,11]. The first is the M’Naghten Rule, which originated in nineteenth-century English law and remains the most traditional and commonly used test [8,11]. Under this rule, a defendant is declared legally insane if, because of a mental illness, they did not understand what they were doing or did not know that their actions were wrong [6,8]. The focus is on cognitive ability and moral awareness [8]. For example, if a person commits a crime while experiencing severe psychosis and believes their actions are justified or not real, they may meet this criterion [8,11]. However, this test only focuses on whether the person understood their actions, not whether they could control them [8].

The second test is the Irresistible Impulse Test, which considers whether the person could control their behavior [8,11]. Here, a defendant is declared legally insane if they understood their actions but could not control their behavior due to a mental illness [8]. The focus is on behavioral control and their ability to resist these impulses [8].

ol and their ability to resist these impulses [8].

Another test is the Model Penal Code test, a more modern standard still used in several jurisdictions [8,11]. In this test, a defendant is considered insane if, due to mental illness, they lacked the ability to understand their actions or the ability to control their behavior [8]. The Model Penal Code essentially combines the goals of the previous two tests [8].

Lastly, the Durham Rule, rarely used today, examines whether the crime was a direct result of mental illness [8,11]. This establishes a causal relationship between mental illness and crime [8]. It is less commonly used because it is seen as too vague and difficult to apply consistently [8,11].

The burden of proof is the obligation of a party in a legal case to provide enough evidence to demonstrate that their claim is valid [3]. This means in order to use an insanity argument, the defense must explicitly prove insanity, as the courts do not automatically assume it [3,6]. Mental evaluations and testimony from qualified professionals are essential, such as psychiatrists and clinical psychologists [8,11]. These evaluations establish credibility for the defendant’s claim, and determine whether they meet the legal standard for insanity at the time of the crime, not just the fact of whether they have a mental illness or not, as this could have developed at a later time [6,8]. Psychiatrists conduct forensic evaluations, interview the defendant, review prior medical and psychiatric history, perform psychological tests, and observe behaviors [8,11]. Then they must testify in court to explain their diagnosis and final evaluation [8]. In the end, a jury decides which side is more convincing. 

Legal insanity is a legal standard determined by the court, and it is not to be confused with a medical diagnosis [6,8]. Legal insanity focuses on whether the defendant was mentally capable of understanding and knowing that their actions were wrong at the time of the crime, which is not a medical diagnosis [6]. The purpose of conducting tests to determine an individual’s sanity is merely for the sake of upholding criminal responsibility, not to diagnose or treat the mental illness as psychiatrists do [8].

Psychological Definition of Insanity

The question of whether or not the insanity plea is constitutional has long been debated [11]. Before analyzing both perspectives, it is necessary to understand what it means to be “insane.” From a psychological perspective, insanity is understood as a disturbance in mental processes rather than simply a legal condition [4,8]. Psychologists focus on how mental illness affects thoughts, emotions, perception, and behavior [4,9]. Psychology analyzes conscious experiences, such as irrational thoughts or distorted perceptions of reality [4]. Psychosis is a condition where a person loses contact with reality, causing hallucinations or delusions [9]. These disruptions may prevent individuals from thinking clearly, remembering accurately, or responding appropriately to their environment [4,9]. In this impaired state, individuals may commit severe crimes without full control over their behavior, and psychosis is among the most common psychological conditions cited in insanity defense cases [7,8].

Psychological theories recognize that severe mental illnesses are influenced by a combination of biological, psychological, and environmental factors [4,9]. These include physical and chemical changes in the brain, genetic predispositions, and abnormalities in brain structure or function that may affect thinking and perception [9]. Exposure to trauma, such as abuse, violence, or extreme stress, can also significantly impact mental health and contribute to the development of psychosis [9]. To meet the criteria for a severe mental illness, a wide range of biological, psychological, and environmental factors must be carefully evaluated, as it is not a simple diagnosis that can be made from just a few tests [8,9]. This complexity challenges the legal system’s ability to assess responsibility, since courts must apply narrow legal standards to conditions that are often medically and psychologically complex [8,11].

Medical insanity refers to a clinical diagnosis made by psychiatrists [8]. The term “insanity” is associated with severe mental illnesses, especially psychotic disorders such as schizophrenia or severe bipolar disorder, based on evaluations and criteria from the Diagnostic and Statistical Manual of Mental Disorders [8,9]. Medical professionals focus on identifying the specific type of mental disorder and its symptoms [8]. Their goal is to understand and treat the individual’s condition from a medical and empathetic standpoint, rather than simply assigning a legal label [4,8].

Court Cases and Legal Debate

The following cases show that courts do not treat mental illness as an automatic excuse, and instead, apply strict legal standards to decide whether a defendant truly lacked criminal responsibility at the time of the offense [6,11]. One of the most famous insanity defense cases is the State of Wisconsin v. Ed Gein (1957). Ed Gein murdered two women and committed disturbing acts involving corpses [1]. He was diagnosed with schizophrenia, as he suffered from severe psychosis and delusions [1,7]. The court found that he was legally insane and not guilty by reason of insanity [1]. Instead of being admitted to a prison facility, Gein was committed to a psychiatric hospital, where he remained until his death [1]. His case illustrates how severe mental illnesses affect criminal responsibility [1,8]. The ruling sparked widespread debate, raising the question of whether a criminal such as Gein deserved a more humane sentence [11]. Cases involving the insanity defense often raise questions about fairness and justice [11]. People argue that allowing defendants to avoid traditional punishment may create the perception that criminals are escaping accountability, which can be especially controversial in cases involving violent crimes [11].

Another prime example was United States v. Hinckley (1982), which was the attempted assassination of President Ronald Reagan [10]. Like Ed Gein, John Hinckley Jr. also suffered from schizophrenia and was deluded into believing his acts would impress actress Jodie Foster, with whom he had developed an obsessive fixation [10]. He was examined by psychiatrists during the trial, who diagnosed him and noted symptoms of severe depression, detachment from reality, and delusions [10]. Some psychiatrists argued that he understood his actions were wrong, but ultimately, the jury found that he was not guilty by reason of insanity [10]. This decision was highly controversial and led to public outrage [10,11]. Hinckley’s verdict led to stricter insanity defense laws because of the public controversy and concerns that the defense was too easy to use [8,10]. Congress passed the Insanity Defense Reform Act of 1984, which made it more difficult for defendants to prove insanity and narrowed the legal definition of insanity [8,10]. The law shifted the burden of proof to the defense, requiring defendants to provide clear and convincing evidence to support their claim [3,8].

A more modern case to understand is People v. James Holmes (2015). James Holmes opened fire in a movie theater in Aurora, Colorado, killing twelve people and injuring more [2]. Holmes had a medical history of severe mental illness, including schizophrenia and psychosis [2]. His defense argued that due to his delusions, his mental illness prevented him from understanding the wrongfulness of his actions [2]. However, the jury ultimately rejected the insanity plea and found him guilty of multiple counts of murder, to which he was then sentenced to life in prison without the possibility of parole [2]. This is because the legal standard for insanity requires more than just having a mental illness [6,8]. The court must determine whether the defendant was unable to understand their actions or did not know that their actions were wrong at the time of the crime [6]. In this situation, the insanity plea was rejected because the prosecutors argued that Holmes had premeditated the attack, purchased weapons in advance, and prepared for this act [2]. Even though he had a mental illness, the court ruled that his condition did not affect his actions and he was fully aware of what he was doing and how to prepare for it [2]. A history of mental illness alone is not sufficient to establish legal insanity [6,8].

Although the insanity defense is often criticized as a loophole, it is used in less than one percent of criminal cases and succeeds even less often [5]. This shows that mentally ill defendants are not easily excused from accountability; instead, courts require substantial psychological evidence and strict legal proof before removing criminal responsibility [5,6]. Mental illness exists on a wide spectrum, but the law looks at it from a much narrower perspective to determine criminal responsibility [8,11]. This ensures that the insanity defense is reserved only for individuals whose mental illness truly prevents them from understanding their actions or distinguishing right from wrong [6,8]. However, there will always be people who are unhappy with a ruling, and that raises other ethical and legal concerns about how the justice system should balance accountability [11]. The insanity defense remains a necessary but cautious legal procedure [8,11]. It reflects that punishment is not always appropriate when severe mental illness removes a person’s ability to fully understand or control their actions [8]. Rather than serving as a loophole, it is a narrow defense used only in rare cases under strict legal standards [5,6]. Mentally ill defendants do face justice, but in a way that also recognizes the role of mental illness [8,11]. As psychological research advances, the legal system must continue to evaluate how mental illness should be considered in determining criminal responsibility, while ensuring that justice remains fair and balanced [8,11]. Future legal reform and research should focus on improving how courts evaluate severe mental illness while still protecting public safety and maintaining accountability [8,11].

Sources

[1] Avinger, Charles. “Ed Gein.” EBSCO Research Starters, 2022. https://www.ebsco.com/research-starters/history/ed-gein. 

[2] “Burden of Proof: Colorado’s Insanity Plea Rules and the James Holmes Trial.” News Corps, University of Colorado Boulder. May 22, 2015. https://www.colorado.edu/initiative/newscorps/2015/05/22/burden-proof-colorados-insanity-plea-rules-and-james-holmes-trial.

[3] “Burden of Proof.” Wex. Legal Information Institute, Cornell Law School. https://www.law.cornell.edu/wex/burden_of_proof.

[4] Hart, Bernard. The Psychology of Insanity. Cambridge: Cambridge University Press, 1925. http://hdl.handle.net/2346/47063.

[5] “In Support of the Insanity Defense.” Mental Health America. https://mhanational.org/position-statements/in-support-of-the-insanity-defense/.

[6] “Insanity Defense.” Wex. Legal Information Institute, Cornell Law School. https://www.law.cornell.edu/wex/insanity_defense. 

[7] “Mad or Manipulative: The Insanity Defense and the Shadow World of Serial Killers.” International Journal for Multidisciplinary Research 7, no. 3 (2025). https://doi.org/10.36948/ijfmr.2025.v07i03.44599.

[8] Math, Suresh Bada, Channaveerachari Naveen Kumar, and Sydney Moirangthem. “Insanity Defense: Past, Present, and Future.” Indian Journal of Psychological Medicine 37, no. 4 (2015): 381–387. https://doi.org/10.4103/0253-7176.168559. 

[9] “Mental Disorders.” World Health Organization. September 30, 2025. https://www.who.int/news-room/fact-sheets/detail/mental-disorders. 

[10] “Trial of John W. Hinckley, Jr.: An Account.” University of Missouri–Kansas City School of Law. https://law2.umkc.edu/faculty/projects/ftrials/hinckley/hinckleyaccount.html. 

[11] White, Mark D., ed. The Insanity Defense: Multidisciplinary Views on Its History, Trends, and Controversies. New York: Bloomsbury Publishing USA, 2017. ProQuest Ebook Central.