Mental Illness:  Plea of Insanity

Mental illness or pleading mentally instability at the time of committing a crime is an often used defense to a criminal violation. What does it really mean to be “mentally unstable” at the time of committing a crime?

Mental Illness Defined

Pleading not guilty by means of insanity means that the accused admits to committing a crime he or she was charged with, but he or she did not realize that what they were doing was wrong at the time.

Testing Mental Illness

Some states use what is known as the McNaghten Test, which is the test that determines if an offender is insane if mental illness prevents the offender from knowing the difference between right and wrong. Other states have adopted a different test known as the Brawner Test. This test was designed to detect if the accused is insane if, because of mental disease or defect, they lack the substantial mental capacity to fully understand and comprehend the criminality of their actions or to conform their behavior to legal requirements. These tests were both created to test the mental capacity and capability of the accused.

What states accept the mental illness defense?

There are four states that do not accept the mentally insane defense. Kansas, Idaho, Montana, and Utah are those four states. Other states use either the McNaghten or Brawner tests to determine if the accused is mentally stable or unstable. Georgia uses a modified version of the McNaghten Rule. The burden of proof is on the defendant. A guilty, but mentally ill, verdict is allowed.

What are the legal questions surrounding capital trial?

There are several questions and requirements that someone must attest to in order to be able to withstand trial. The first of the first requirement is to make it through police interrogation. Those who are suffering from a mental illness are more susceptible to giving false confession under police pressure. The following traits and characteristics that are associated with mental illness can lead to false confessions: impulsivity, deficits in cognitive processing, suggestibility, delusions and extreme compliance. People who have a mental illness do not comprehend the Miranda rights when they are read to them, thus waiving the right to counsel and not understanding that anything they say can and will be held against them.

One of the questions that someone has to answer with their actions and responses to questions that are asked to them is if he or she is competent to stand trial? A defendant (or the accused) must be competent to stand trial under the United States Constitution. A hearing is held called a competency hearing to determine if the defendant has a “rational as well as factual understanding of the proceedings and whether or not the defendant has the ability to consult with his or her attorney with a reasonable degree of rational understanding. If at a competency trial the judge finds that the accused is not mentally capable of withstanding trial, he or she will more than likely be transferred to a mental hospital where specialists and doctors will try to improve the individual’s mental state to where he or she can meet the competency standard to withstand trial for the crime he or she committed.

Another question that has to be answered and proven by the defense is was the defendant really mentally insane? As previously stated, there are four states that have done away with the mentally insane plea, but among the different states, there are different requirements that the defense has to meet to prove that the accused is (a) mentally insane, (b) mentally diseased, (c) mentally defected, or (d) all of the above.

The ability to form criminal intent is another requirement. Most capital murder statutes require that the State prove beyond a reasonable doubt that the defendant specifically intended to kill the victim. However, many capital defendants who suffer from mental illness lacked any kind of ability to form a specific intent to kill at the time of their committed offense.

Mitigation comes at the penalty phase of the trial. Mitigating evidence is entitled to be presented by the defense to alter or change the verdict.

Mental Illness & Execution

It has been proven to be unconstitutional to give someone the death penalty that is mentally retarded, but there has not yet been a ruling about someone who was mentally unstable at the time a crime was committed. However, the courts have said that it is unconstitutional to execute someone who is mentally unstable at the time of his or her execution.


Mental illness is the number one defense in capital trials. Being mentally ill at the time of committing a crime means that the person committing the crime did not know right from wrong. There are two tests that can determine if a person is mentally ill or not. There are four states that do not accept the plea of mental insanity as a plea at all in defense to a crime. There are five questions and requirements that must be met in order for someone pleading insanity to stand trial. Also, it has been deemed unconstitutional for someone who is mentally insane to be executed while they are still deemed mentally insane.