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Ronald Schouten, M.D., J.D.
Ronald Schouten M.D., J.D.

The Insanity Defense

An intersection of morality, public policy, and science.

There are times when the insanity defense, with all the controversy that surrounds it, is in the news. This is one of those times:

  • It is highly likely that James Holmes, who is facing 142 felony counts in connection with the Aurora, Colorado shootings on July 22, 2012, will raise an insanity defense. First, he’ll have to be found competent to stand trial, which is a separate issue.
  • Anders Breivik admitted to killing 77 Norwegians in July 2011 in a carefully prepared bombing and mass murder, which he claimed was an act of self-defense against Islamization and multiculturalism in Norway. On August 24, 2012, he will learn the court’s verdict. Prosecutors urged the court to find Breivik legally insane, as this would lead to a lifetime of confinement in a mental hospital. Breivik argued against an insanity verdict because, under Norwegian law, he could conceivably be released from prison someday if found guilty.
  • Clayton Osbon, the JetBlue pilot who disrupted a March 27, 2012 flight from Las Vegas to New York by screaming about terrorists and religion, was found not guilty by reason of insanity on July 3, 2012.

What Is the Insanity Defense?

For a person to be convicted of a crime, the prosecution must prove not only that the person engaged in a guilty act (actus reus), but also that he or she had guilty intent (mens rea). If a person does not have criminal intent during an act, no crime occurs: a person who takes someone else’s property, honestly believing it is his own, is not guilty of larceny.

But what about situations in which the person commits the act, and intended to do so, but was suffering from a mental or physical condition that impairs their ability to appreciate that they are doing something wrong or to control their behavior? That’s where the insanity defense comes in.

While the insanity defense is a legal doctrine, at its heart it is the expression of a moral principle found in societies across time and multiple cultures: Individuals should not be punished for their otherwise criminal acts if they lack certain characteristics that relate to the ability to engage in rational thinking, including an appreciation of the wrongfulness and consequences of their actions, or control their behavior.

Take, for example, children. A 5-year-old who sets fire to the drapes because the flames are pretty will not be charged with arson when the house burns down. The same is true for people with severe developmental disabilities. And what about people who cause harm to others or commit crimes while sleepwalking? Yes, those cases exist, and the defendants are generally not held criminally responsible.

The legal requirements for the insanity defense have varied over the centuries and societies in which it has existed. Here in the United States, public outrage in response to successful insanity defenses in high profile cases has often led to changes that limit the availability of the defense and its likelihood of success.

For example, in the early 1980s, the standard for the insanity defense in federal criminal cases was the American Law Institute/Model Penal Code standard. It provides for acquittal on the basis of insanity if, as the result of mental disease or defect, the defendant lacked substantial capacity to appreciate the wrongfulness of his actions or lacked substantial capacity to conform his behavior to the requirements of the law.

This was considered to be more lenient than the standard that had been used until then. But, after John Hinckley was found not guilty by reason of insanity for his failed assassination attempt on President Ronald Reagan, the federal standard was changed to a stricter version that limits the defense to those with severe mental illness and those who are unable to appreciate the wrongfulness of their conduct. Thus, the new federal standard eliminated the volitional component and left only the cognitive component. Many states have followed suit and some have eliminated the insanity defense altogether.

Regardless of the precise legal standard, the insanity defense is rarely raised and even more rarely successful. It is used in only about 1% of cases in the U.S. and is successful less than 25% of the time.

What Qualifies as a “Mental Disease or Defect” for the Insanity Defense?

While any mental or medical condition could theoretically serve as a basis for an insanity defense, the law limits the conditions that can be considered for that purpose. These restrictions are aimed at ensuring that only those who truly deserve to be relieved of responsibility are eligible for it.

To that end, voluntary intoxication is excluded, as are conditions that have antisocial behaviors as their primary characteristic; e.g. kleptomania, pyromania, and pedophilia, and appear to have no physiological basis. Some legal standards require that the mental illness serving as the basis for the defense be “severe.”

Not every condition that qualifies to be the basis for an insanity defense has an equal chance of succeeding in achieving an acquittal. Those that succeed tend to be marked by either severity or evidence that they arise from a physiological, as opposed to a purely psychological, disorder. These are, for example, mental illnesses that severely affect a person’s perception of reality or, in some jurisdictions, the ability to control their behavior. They include psychoses, severe depression, mania, or anxiety disorders like posttraumatic stress disorder (PTSD). An argument that an act of violence was the result of a traumatic brain injury causing irritability and poor impulse control is more likely to be convincing than the assertion that the violence arose from personality disturbance.

How Will Advances in Neuroscience and Genetics Affect the Insanity Defense?

The presence of abnormal brain function due to injury, tumor, and epilepsy has been successfully offered as the basis for an insanity defense in a number of criminal cases for hundreds of years. When it has been successful, the apparent key to the success of these defenses lies in the concrete and observable nature of the abnormality: Juries can see the tumor on a brain scan and may be presented with evidence that the criminal behavior did not occur before the injury or that it stops after treatment.

Advances in neuroscience and genetics provide a means for less obvious brain abnormalities to be offered as the basis for a defense. And this presents a challenge to traditional notions of the causes of mental illness, as well as some types of criminal behavior. There is growing evidence for genetic transmission of numerous psychiatric conditions, including personality disorders, as well as their underlying anatomic and physiological abnormalities.

Psychopathy, for example, is an extreme form of personality disturbance, with no established effective treatment, marked by indifference to right and wrong, lack of empathy, conning and manipulation, and aggressive pursuit of self-interest. It is associated with criminal behavior of all sorts, including crimes of extreme violence in some cases. As such, it has been excluded from consideration as the basis for an insanity defense.

But discoveries of fundamental anatomical and physiological differences between the brains of psychopaths and non-psychopaths — including non-psychopathic criminals — as well as evidence those psychopathic traits may be inherited, has set the stage for arguments that even those who commit the worst of crimes should not be held responsible for them. After all, they didn’t choose their genetic makeup or to be born without the capacity for empathy. The current issue of Science contains a report that while a diagnosis of psychopathy may result in longer criminal sentences, judges seem inclined to impose more lenient sentences where evidence of a biological basis for the defendant’s psychopathy was introduced.

So far, these new arguments have failed in preventing guilty verdicts. But as the evidence mounts, we can expect to see more such arguments, and perhaps more leniency in sentencing. When, and if, the insanity verdict is extended to individuals with psychopathy, society must be prepared for the next question: What do we do with those who are not criminally responsible, but who are too dangerous to live in society and for whom there is little, if any, effective treatment? It will be a fascinating debate that challenges our notions of justice, morality, and science.

About the Author
Ronald Schouten, M.D., J.D.

Ronald Schouten, M.D., J.D., is an associate professor of psychiatry at Harvard Medical School and director of the Law & Psychiatry Service at Massachusetts General Hospital.