In a criminal case, a defendant will often seek to plead the insanity defense. An insanity defense may be a particularly attractive option if the murder was especially egregious or heinous. But while pleading insanity can be a viable defense for certain defendants, courts of law do not accept insanity pleas from every defendant. In order for a defendant to pleas insanity successfully, the defendant must show that 1) the defendant did not know that what he did was wrong, and 2) that the defendant failed to act with the necessary mens rea requirement (Fradella, 2007, p. 9). These basic elements are derived from the M’Nagten rule, which focuses on the defendant’s diminished cognitive and moral capacity (Clark v. Arizona, 2006, p. 750-751).
At both the federal and state level, the defendant proffering the insanity plea bears the initial burden of proof (Miller, 1985, p. 353). Since insanity is an affirmative defense, the defendant must prove by clear and convincing evidence all elements of the defense (Miller, 1985, p. 385). While the government must prove all elements of a crime beyond reasonable doubt, the insanity defense is an exception to the general rule that places the burden on the defendant, rather than the government (Miller, 1985, p. 354).
For a defendant to be guilty of a crime, it requires there be both actus reus and mens rea. The actus reus refers to the criminal act. The criminal act is satisfied by the sheer fact that a crime was committed. When a victim is murdered or raped, this is a criminal act. However, to be held legally responsible for one’s crimes, a defendant must also possess the necessary mens rea. This requires the defendant to have a “guilty mind,” which means that the defendant acted with intent. The idea of mens rea has existed since ancient civilizations (Miller, 1985, p. 338). The idea behind mens rea is that to be criminally responsible for a crime, the defendant must recognize the difference between right and wrong. Not guilty by reason of insanity is a legal term and denotes that while the defendant committed the crime, the defendant did not have the requisite intent, or mens rea, to be found legally guilty.
References
Clark v. Arizona, 548 U.S. 735 (2006).
Fradella, H. F. (2007). From insanity to beyond diminished capacity: Mental illness and criminal
excuse in the post-clark era. University of Florida Journal of Law and Public Policy, 7-
92.
Miller, H.T. (1985). Recent changes in criminal law: The federal insanity defense. Louisiana
Law Review, 337-360.
