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Insanity Defense

Today I will discuss an aspect of the defense of insanity to a crime.

By
Michael W. Flynn
3-minute read

First, a disclaimer: Although I am an attorney, the legal information in this podcast is not intended to be a substitute for seeking personalized legal advice from an attorney licensed to practice in your jurisdiction. Further, I do not intend to create an attorney-client relationship with any listener.   

Today I will discuss an aspect of the defense of insanity to a crime. Tracy from East Melbourne, Australia wrote:

Hi, Legal Lad. I'm confused about the insanity defense. If it's obvious that a person committed a crime (say, murder), but is also obviously mentally incapable of understanding his/her actions, why isn't that person GUILTY by reason of insanity? Why is it always NOT GUILTY by reason of insanity?

This question really jumped off the page for me because it does seem odd on a practical level that someone who kills another human being could be “not guilty” simply because he is nuts. 

Almost all crimes require both an actus reus, and a mens rea. Actus reus refers to the criminal act, while mens rea refers to the “guilty mind.” In common law countries such as the United States, the United Kingdom, and Australia, the test of criminal liability is usually expressed in the Latin phrase, “actus non facit reum nisi mens sit rea,” which means that “the act does not make a person guilty unless the mind is also guilty.”

In the context of murder, the government must first prove the actus reus. That is, the government must prove, beyond a reasonable doubt, that the defendant actually killed somebody.

The government must also prove that the defendant intended mentally to commit the illegal act. There are varying degrees of intent for homicide that result in varying charges and punishment. For example, consider the defendant who creates an elaborate plot to murder his wife with arsenic over the course of several months. Now consider the defendant who, while working on a construction site, accidentally drops a hammer that falls 40 stories, killing his wife who happens to be passing underneath.

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