You've probably seen many movies and television shows where a defendant's attorney wants to enter an insanity defense. However, this is not a common defense, mainly because it takes a lot to prove that someone meets the criteria for an insanity defense.
A person may have a successful insanity defense if he or she meets one of two definitions:
-- The defendant has a mental disease or defect at the time of the crime that does not allow him or her to be able to distinguish right from wrong. However, this mental state is not to be confused with someone whose "mental disease or defect with moral obliquity, mental depravity, or passion [that grew] out of anger, revenge, hatred, or other motives."
-- The defendant has a mental disease or defect that prevents him or her from forming the necessary mental state needed for an element of the charged crime. Just as in the first definition, this mental state is not be confused with someone whose mental disease or defect with moral obliquity, mental depravity, or passion growing out of anger, revenge, hatred, or other motives."
The law specifically states that the voluntary ingestion of alcohol or another psychoactive substance is not enough for an insanity criminal defense.
If the defense introduces some evidence that the defendant is not fit to stand trial because of an insanity defense, the prosecution must then prove that the defendant is sane -- beyond a reasonable doubt.
There are many evaluations that must be completed before an insanity defense can proceed. These include psychiatric evaluations, polygraphs and narcoanalytic drugs.
While the insanity defense is not something that most people can use at trial, there are some defendants that it may help. An experienced criminal defense attorney in Colorado can provide more information on this special type of defense strategy.
Source: Colorado Bar Association, "Insanity" Dec. 09, 2014