While the insanity defense may be one of the better known defense tactics used during criminal trials, it also one of the least common and least successful. It is a rare tactic, because there is much confusion around what it means to be criminally insane, and whether mental illness would qualify as a valid excuse.
Why Mental Illness Isn't Enough
If the defendant of a criminal trial has struggled their whole life with a diagnosable mental illness, it may seem obvious that their mental illness contributed to their crime, but that's not always true.
To better understand why mental illness isn't enough, it's important to understand the definition of insanity. At the very minimum, insanity may be defined as the inability to understand the wrongness of an act. While mental illness can certainly contribute to the state of mind of an individual during a crime, they may still be fully aware of the wrongness of their actions.
What it Takes to Prove Insanity
The definition of insanity varies from state to state, and even between the states and the federal government. So how can an insanity defense be proven if the definition is so subjective?
As mentioned above, true insanity usually means the defendant was unable to distinguish between right and wrong. This can occur as a result of lifelong mental illness or due to a momentary lapse in sanity where the defendant wouldn't otherwise be considered mentally ill. Proving this, however, is difficult and time consuming, and it requires a clear and convincing argument that the defendant was insane during the time of the crime – in other words, the defense must show that there is no other explanation for the actions of the defendant, and that they were unaware of the wrongness of said actions.
How Common is the Insanity Defense Tactic?
Due to the rarity of the insanity plea, those cases that do use it as a defense may become highly sensationalized. This leads to people assuming it's a much more common defense tactic than it really is.
While statistics vary from state to state, on average, the defense is used in less than 1% of criminal cases, and even within those, only a fraction are upheld. This means that the defense is not only one of the least commonly used, but also one of the least successful tactics available to criminals.
As treatment and awareness of mental illness continues to improve, it may be easier for individuals to begin to understand the difference between mental illness and insanity, and why being mentally ill doesn't automatically qualify one for the insanity defense. Until then, the insanity defense will continue to be a highly sensationalized (and misunderstood) phenomena within the world of criminal defense. If you have questions about a case or law in general, visit an attorney like McKone & Unruh.