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Insanity Defense

In California, a criminal defendant is entitled to an acquittal if it is determined that she was legally insane at the time she committed a crime. This occurs where a mental disease or defect prevents the defendant from mentally establishing the mens rea required to commit the criminal offense (CalCrim No. 3450)

Note: Mens rea is the knowledge of wrongdoing that makes up a part of most crimes. If a person can not intend to commit an act, or know of the wrongdoing of her act, due to a mental disease or defect, then she is entitled to an acquittal of the criminal charges.

In criminal law, a criminal defendant is considered insane if at the time she committed the crime she is so impaired by mental disease or illness that she did not know the nature and quality of her act or that her conduct was morally wrong.

A defendant does not know the nature and quality of her act when she does not understand its physical nature and consequences.

For example, the defendant is not guilty by reason of insanity of the crime of vehicular manslaughter, if the defendant, as a result of a mental disease or defect, truly believed that she was driving a vehicle in a NASCAR video game, when in reality, she killed another person when she drove her real vehicle into oncoming traffic. In this situation, the defendant’s mental disease or defect precludes her from understanding what is actually happening.

Example II: The defendant is not guilty by reason of insanity of the crime of theft, if the defendant, as a result of a mental disease or defect, does not know that taking another person’s personal property without consent or legal justification is morally wrong.

Note: The defendant does not have to show both factors are present in her insanity defense. In other words, she does not have to prove that she 1) did not understand the nature and quality of her act, and 2) she lacked an understanding that her conduct was morally wrong; the defendant has to show only one set of facts or the other for her insanity defense claim to be applicable.

Defense Limitations: One of the limitations to an insanity defense is that the criminal conduct must have resulted from a mental disease or defect. In essence, the defendant cannot claim that she committed a crime as a result of insanity if she understood the nature and consequences of her criminal conduct and that she also knew her criminal conduct was morally wrong, even if she actually suffers, coincidentally, from a mental illness. Consider this situation: If the defendant, as a result of schizophrenia (mental illness), hears imagined voices that instruct her to commit an illegal act, and she knows the nature and consequences of the act she was instructed to commit, and she understands that the act is morally wrong, then there is no reason to consider her schizophrenia as a defense because it does not matter if the voices were imaged or real. In other words, a person is not entitled to engage in criminal conduct with complete immunity just because she coincidentally suffers from a mental disease or defect.

Temporary insanity: It is possible for a defendant to be temporarily insane. In other words, the defendant is determined to be insane during the commission of the alleged offense, but she is not normally determined to be insane. This sometimes occurs when the defendant ingest an intoxicating drug or chemical, either voluntarily or involuntarily, that renders the defendant legally and temporarily insane.

Note: It is not considered temporary insanity simply because the defendant is very upset at the time of the alleged offense. In order for the defense of temporary insanity to prevail the defendant will be required to prove that the insanity was settled, which means the disease or defect of the mind lasts beyond the time it takes for any intoxicants to naturally be expelled from the defendant’s body, or for the extrinsic factor that lead to temporary insanity to pass. Consider the following: Severe intoxication can lead to an insanity defense if the defendant’s mental status reaches the definition for legal insanity, but that temporary insanity defense vanishes once the defendant is sufficiently sober that she no longer meets the legal definition of insanity. On the other hand, chronic alcoholism that has permanently diseased the defendant’s mind might be considered permanent, and thereby render the defendant legally insane even when there is no actual alcohol in the defendant’s blood.

Insanity Previously Settled: A prior commitment or adjudication of insanity may lead to a presumption of insanity at the time of the crime committed. A district attorney may argue against that presumption where there is evidence that suggests the defendant does not meet the criminal law definition of legal insanity at the time of the alleged offense...despite the fact that the defendant has previously been committed for, or adjudicated to be, insane.

Competency to Stand Trial: Competency to stand trial deals with the defendant's mental state at the time of trial, not at the time that the crime was committed. It is a complete defense to a criminal act if a person is found to be legally insane at the time the crime was committed. However, a criminal trial may not even progress to that issue if the defendant is incompetent to stand trial. Whether or not a defendant is competent to stand trial is determined by a present sanity test. The present sanity test includes an assessment of the defendant’s ability to understand the purpose of the proceedings against her and whether or not she is capable of assisting her criminal defense attorney.

Separate Trials: In California, the issue of whether or not a person was legally insane during the commission of the alleged offense is not made part of the same trial where the defendant is prosecuted. Rather, a separate trial on the issue of sanity is held after a criminal conviction. At the trial on the issue of sanity, a defendant has the burden of proving by a preponderance of evidence that she was legally insane during the commission of the alleged offense. However, the court must have received some evidence of the issue of mental disease or defect in the underlying trial before the court will grant a subsequent trial on the issue of insanity defense. This means you cannot bring up a insanity defense without eliciting at least some evidence related to that issue during the underlying trial.

Note: Proof by a preponderance of the evidence means more likely than not. It is a lower burden of proof than the beyond a reasonable doubt standard, which is the burden that is placed on the prosecutor in the underlying trial. One of the reasons for having a separate trial on the issue of insanity is to help the jury keep the burden correctly placed on the correct party and to clear up the level of proof required by the respective parties.

Commitment Issues: The defendant will be committed to a mental hospital for the criminally insane if she is found not guilty by reasons of insanity. She will be committed until such time that her mental condition has improved and she is determined to no longer be a danger to herself or others. When a defendant is found to be incompetent to stand trial she may be committed to a mental hospital until she has regained her competency to stand trial, if ever; thereafter, her trial will resume.

Note: When a defense attorney has reason to doubt the defendant’s competency to stand trial the defense attorney will raise that issue with the court and the defendant will be delivered to a psychiatrist for a medical evaluation on the issue. If the psychiatrist determines that the defendant is competent to stand trial then the psychiatrist will deliver that information to the court and the court will decide the issue.


Also, the defendant might not earn as many good behavior credits towards reducing any jail or prison sentence when a defendant is subjected to psychiatric or psychological evaluations in a criminal case (assuming the defendant is convicted and sentence to jail or prison for the underlying crime). This is true despite the fact that the defendant is not ordinarily allowed to leave the custody of the sheriff or the psychiatrist during the evaluation process.

For more information on the defense of insanity, and defenses to criminal charges in general, contact our law offices for a free consultation. Our criminal defense lawyers are always available to answers you defense options and explain your rights. Call today!


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