Commentators have noted that the insanity defense is risky for criminal defendants because it virtually eliminates any possibility that prosecutors will agree to a plea bargain. Studies, including an eight-state investigation by the National Institute of Mental Health, have shown that the insanity defense is raised in less than one percent of all felony cases. This defense is successful in only a fraction of those cases.
Nevertheless, when the insanity defense is raised, it continues to spur controversy. For instance, in 2001, Andrea Yates of Texas, who allegedly suffered from a mental illness, drown her five children in less than an hour. At her trial for capital murder, Yates’ attorneys pleaded the insanity defense, arguing that she suffered post-partum depression. A jury rejected this argument and found her guilty. She received a life sentence for the murders.
The public showed great interest in the Yates trial. Some members of the public, especially but not limited to women’s groups, sympathized with Yates due to her battle with post-partum depression. At her trial, four out of five psychiatrists and one psychologist testified that Yates did not know right from wrong. However, the single mental health expert called by the prosecution testified that Yates indeed knew right from wrong, and the jury eventually rejected her insanity defense. Facts later revealed that the state’s expert had presented false testimony regarding Yates, and a Texas appellate court in 2005 reversed her conviction and ordered a new trial. Yates v. State, 171 S.W.3d 215 (Tex. App. 2005).
The Yates case demonstrates that in some instances the insanity defense can garner some support. Nevertheless, such a defense is still difficult to prove, and states have not made significant efforts to revise their versions of the insanity defense in recent years.