Most states have long recognized a form of the insanity defense, based on the defendant’s mental illness, defect, or inability to understand that the criminal act was wrong. In pleading an insanity defense, the defendant admits the criminal conduct, but asserts a lack of culpability based on mental illness. Many states still model their insanity defense on the old English rule of law (the M’Naghten rule from 1843) in which the defendant asserts he (1) did not know the nature and quality of the act, or (2) did not know that it was wrong.
And it is an affirmative defense to a prosecution under any federal statute (federal law) that, at the time of the offense, the defendant was unable to appreciate the nature and quality of his acts, or the wrongfulness of his acts. See 18 U.S.C. §17.
When a defendant is found not guilty by reason of insanity it does not mean he necessarily goes free. States often have requirements for treatment or institutionalization after such a finding. And some states require, at a minimum, confinement in a treatment institution or facility for the length of time the person would have received if convicted—so a defendant may end up spending more time confined than if he did not raise such a defense.
The law regarding the availability, definitions, and nature of the insanity defense vary from state to state, and are usually located in a state’s statutes.
In Ohio, the insanity defense is recognized and is similar to the M'Naghten rule, which is the traditional standard for insanity defenses. Under Ohio law, a defendant may be found not guilty by reason of insanity if at the time of the commission of the offense, due to a severe mental disease or defect, they did not know the wrongfulness of their actions. This is codified in Ohio Revised Code Section 2901.01(A)(14) and 2945.39. The burden of proof is on the defense to establish insanity by a preponderance of the evidence. If a defendant is found not guilty by reason of insanity, Ohio law requires that the court hold a hearing to determine if the individual should be committed to a mental health facility for treatment. The length of commitment can vary, but it may be for a period equivalent to the potential prison sentence or longer, depending on the individual's recovery and the risk they pose to public safety. Federal law, as stated in 18 U.S.C. §17, also allows for an insanity defense, requiring that the defendant was unable to appreciate the nature and quality or the wrongfulness of their acts at the time of the offense.
