Some of the most famous insanity defense cases in American criminal law ended in acquittal, and some ended in conviction despite undisputed severe mental illness. John Hinckley Jr., Andrea Yates, and Lorena Bobbitt were found not guilty by reason of insanity. Jeffrey Dahmer, Eddie Ray Routh, and Eric Clark were not. The difference between these outcomes usually comes down to two things: which legal test the jurisdiction uses, and whether the jury believes the defendant understood that what they were doing was wrong.
Cases Where the Insanity Defense Succeeded
Richard Lawrence (1835)
The first high-profile American insanity acquittal came in 1835, after Richard Lawrence, an unemployed house painter, tried to shoot President Andrew Jackson outside the U.S. Capitol. Both pistols misfired. Lawrence believed he was the King of England and that Jackson was blocking money owed to him. The jury acquitted him by reason of insanity, and he spent the rest of his life in psychiatric institutions.
Daniel M’Naghten (1843)
The case that gave American insanity law its most enduring test was actually British. In 1843, Daniel M’Naghten shot and killed Edward Drummond, private secretary to Prime Minister Robert Peel, believing Drummond was Peel himself. M’Naghten suffered from paranoid delusions that Peel’s political party was persecuting him. His acquittal outraged the British public and prompted the House of Lords to formulate the M’Naghten Rules, which remain the baseline insanity test in a majority of American jurisdictions.
John Hinckley Jr. (1982)
On March 30, 1981, John Hinckley Jr. shot President Ronald Reagan and three others outside a Washington, D.C., hotel. Hinckley was delusional, convinced that assassinating the president would impress actress Jodie Foster. After a seven-week trial in 1982, the jury found him not guilty by reason of insanity on all thirteen counts.
At the time, federal law required prosecutors to prove the defendant was sane beyond a reasonable doubt, and the jury concluded the government had not met that burden. Hinckley was committed to St. Elizabeths Hospital, a federal psychiatric facility, where he remained for 35 years. He was conditionally released in 2016 and granted unconditional release in June 2022. The verdict itself drove the largest overhaul of insanity defense law in American history.
Lorena Bobbitt (1994)
In 1994, Lorena Bobbitt was acquitted by reason of temporary insanity after severing her husband’s penis with a kitchen knife. Her defense presented evidence of prolonged domestic abuse and argued that she suffered a brief psychotic episode triggered by years of physical and sexual violence. The jury of seven women and five men found her not guilty of malicious wounding, a charge that carried up to 20 years in prison. She was committed to a state psychiatric hospital for evaluation and released after 45 days.
Andrea Yates (2006)
Andrea Yates drowned her five children, ages six months to seven years, in the family bathtub in Houston, Texas, on June 20, 2001. Her first trial in 2002 resulted in a murder conviction, but that verdict was overturned on appeal after an expert witness admitted to providing inaccurate testimony. At her second trial in 2006, a jury found her not guilty by reason of insanity. Yates had a documented history of severe postpartum psychosis and had been hospitalized multiple times before the killings. Medical experts testified that she was actively psychotic before, during, and after drowning her children. She was committed to a state psychiatric facility, where she has remained.
Cases Where the Insanity Defense Failed
Jeffrey Dahmer (1992)
Jeffrey Dahmer confessed to murdering 17 men and boys between 1978 and 1991, many of whom he dismembered and partially consumed. He pleaded not guilty by reason of insanity. The prosecution countered that Dahmer’s methodical efforts to avoid detection, including disposing of evidence and lying to police, proved he understood exactly what he was doing and knew it was wrong. The jury agreed and found him guilty. The case is often cited as an example of why juries resist insanity verdicts in cases involving especially horrific crimes, regardless of how disturbed the defendant appears to be.
Eddie Ray Routh (2015)
Eddie Ray Routh shot and killed Chris Kyle, the former Navy SEAL known as the “American Sniper,” and Kyle’s friend Chad Littlefield at a Texas shooting range in February 2013. Routh’s defense argued insanity, pointing to his diagnosis of PTSD and a psychotic episode at the time of the killings. Under Texas law, insanity requires proof that the defendant did not know their conduct was wrong as a result of severe mental disease or defect.1Texas Courts. Charge of the Court – State of Texas vs. Eddie Ray Routh The jury rejected the insanity claim after deliberating for less than three hours, finding Routh guilty of capital murder.
Eric Clark (2000)
In 2000, seventeen-year-old Eric Clark, who suffered from chronic paranoid schizophrenia, shot and killed Flagstaff police officer Jeffrey Moritz. Clark believed that aliens had invaded earth and were impersonating government officials. Despite no dispute that Clark was actively psychotic at the time, the trial judge convicted him of first-degree murder, concluding that Clark had not proven his schizophrenia distorted his perception so severely that he did not know his actions were wrong.2Justia Law. Clark v. Arizona, 548 U.S. 735 (2006)
Clark appealed to the U.S. Supreme Court, arguing that Arizona’s narrow insanity test, which considered only whether he knew his actions were wrong and ignored whether he understood the nature of his act, violated due process. The Court disagreed and upheld his conviction, ruling that states have wide latitude to define their own insanity standards.2Justia Law. Clark v. Arizona, 548 U.S. 735 (2006) Clark was sentenced to life in prison without the possibility of release for 25 years. Even severe, undisputed mental illness does not guarantee an insanity acquittal.
Why Similar Facts Produce Different Verdicts
No single insanity standard applies everywhere in the United States. The test a court uses shapes which defendants qualify.
The oldest and most widely used comes from M’Naghten’s case. Under this “right from wrong” standard, a defendant is legally insane only if a mental disease prevented them from understanding what they were doing or from knowing it was wrong. The focus is entirely cognitive and ignores whether the person could control their behavior.
Some states add the irresistible impulse test, which covers situations where a defendant understood their actions were wrong but a mental illness made it impossible for them to stop themselves. Knowing something is wrong and being able to resist doing it are treated as separate questions.
The Durham Rule, established in 1954, took a broader approach by asking whether the crime was a product of mental illness. Critics argued this gave psychiatrists too much influence over legal outcomes, and today New Hampshire is the only state that still uses it.
The American Law Institute’s Model Penal Code test, developed in 1962, blends the two approaches. It asks whether a mental disease left the defendant without substantial capacity to appreciate the wrongfulness of their conduct or to conform their behavior to the law. Around 21 states have adopted some version of this standard.
How Hinckley’s Acquittal Rewrote the Federal Rule
Public fury over Hinckley’s acquittal pushed Congress to pass the Insanity Defense Reform Act of 1984, which fundamentally restructured the federal defense. Before the Act, federal courts used the broader Model Penal Code test, which allowed acquittal if a defendant could not conform their behavior to the law, even if they knew it was wrong. The new law eliminated that “volitional” prong entirely.
Under current federal law, the insanity defense succeeds only if the defendant proves that a severe mental disease or defect made them “unable to appreciate the nature and quality or the wrongfulness” of their actions. Understanding right from wrong is what matters, not whether the person could control themselves.3Office of the Law Revision Counsel. 18 U.S. Code 17 – Insanity Defense
The Act also flipped the burden of proof. Before 1984, prosecutors had to prove the defendant was sane. Now the defendant must prove insanity by clear and convincing evidence, a significantly harder standard to meet.3Office of the Law Revision Counsel. 18 U.S. Code 17 – Insanity Defense Several states followed the federal government’s lead and tightened their own laws in the years that followed.
How Often the Defense Actually Wins
The insanity defense is raised in roughly one percent of all felony cases, and only about a quarter of those defendants are acquitted. That means approximately one in 400 felony defendants ends up with a not-guilty-by-reason-of-insanity verdict.4Journal of the American Academy of Psychiatry and the Law. The Volume and Characteristics of Insanity Defense Pleas: An Eight-State Study The success rate varies enormously by state, ranging from under 10 percent in some jurisdictions to over 80 percent in others, depending on the legal standard and how courts handle psychiatric evidence.
Most successful cases involve defendants with severe psychotic disorders like schizophrenia. Claims based on personality disorders, substance abuse, or conditions like PTSD face much steeper odds, as the Routh case showed. Juries tend to be skeptical when a defendant’s actions show signs of planning or awareness, even if a genuine mental illness is present.
What Happens After an Acquittal
A verdict of “not guilty by reason of insanity” does not mean the defendant walks free. Under federal law, a person acquitted by reason of insanity is automatically committed to a psychiatric facility for evaluation and likely long-term hospitalization.5Office of the Law Revision Counsel. 18 U.S. Code 4243 – Hospitalization of a Person Found Not Guilty Only by Reason of Insanity Most states have similar commitment procedures.
Within 40 days of the verdict, the court orders a psychiatric evaluation. If the evaluation shows that releasing the person would create a substantial risk of bodily injury to others or serious property damage, the court commits them to the custody of the Attorney General for treatment in a secure facility.5Office of the Law Revision Counsel. 18 U.S. Code 4243 – Hospitalization of a Person Found Not Guilty Only by Reason of Insanity
Getting released is harder than many people expect. For violent offenses, the person must prove by clear and convincing evidence that they have recovered enough that release would no longer pose a substantial risk. For non-violent offenses, the standard drops to a preponderance of the evidence, but confinement can still last years.5Office of the Law Revision Counsel. 18 U.S. Code 4243 – Hospitalization of a Person Found Not Guilty Only by Reason of Insanity
Multiple studies have found that insanity acquittees typically spend longer confined in psychiatric hospitals than they would have spent in prison had they been convicted of the same offense. One eight-state study found that NGRI acquittees spent nearly double the confinement time compared to convicted defendants serving criminal sentences for similar crimes. Hinckley’s 35-year institutionalization is an extreme example, but it illustrates the pattern.
States That Have Abolished the Defense
Four states have eliminated the traditional insanity defense entirely: Kansas, Idaho, Montana, and Utah. Defendants in these states can still introduce mental health evidence to argue they lacked the intent required for the crime, but they cannot be fully acquitted on the basis of insanity.
The Supreme Court addressed this directly in Kahler v. Kansas (2020), ruling that the Constitution does not require states to adopt any particular insanity standard. The decision gave states broad discretion to define, narrow, or even eliminate insanity as an independent defense, so long as defendants retain some ability to present mental health evidence at trial or sentencing.6Supreme Court of the United States. Kahler v. Kansas, 589 U.S. ___ (2020) A defendant with the same diagnosis and the same crime could face a genuine path to acquittal in one state and no insanity defense at all in another.