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.

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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 States—one 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 100—0.85 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 defect—and 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 NGRI—the 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.