Standard for Insanity Plea : California

In California, Section 25 of the Penal Code defines the standards for the insanity plea, which must be proven by a preponderance of the evidence. It requires two conditions for the offender to be found NGRI or not “criminally responsible”: First, the offender must have been, at the time of the crime, incapable of distinguishing between right and wrong. Second, the offender must have been incapable of controlling his or her actions. Consistent with Federal law, proving these conditions is the responsibility of the defendant.

While interpreting the practical application of the law has sometimes been challenging for courts, precedent has made it clear that California is concerned primarily with the mental status at the time of the offense—regardless of whether that mental status is persistent and pervasive: Heavier weight is placed on cognitive considerations (distinguishing between right and wrong and understanding the nature of the act) than on the volition arm (ability to control actions—or “irresistible impulse”). California does not consider “irresistible impulse” as a legal defense.

 

PENAL CODE
SECTION 25-29

25.  (a) The defense of diminished capacity is hereby abolished. In a criminal action, as well as any juvenile court proceeding, evidence concerning an accused person's intoxication, trauma, mental illness, disease, or defect shall not be admissible to show or negate capacity to form the particular purpose, intent, motive, malice aforethought, knowledge, or other mental state required for the commission of the crime charged.

   (b) In any criminal proceeding, including any juvenile court proceeding, in which a plea of not guilty by reason of insanity is entered, this defense shall be found by the trier of fact only when
the accused person proves by a preponderance of the evidence that he or she was incapable of knowing or understanding the nature and quality of his or her act and of distinguishing right from wrong at the time of the commission of the offense.

   (c) Notwithstanding the foregoing, evidence of diminished capacity or of a mental disorder may be considered by the court only at the time of sentencing or other disposition or  commitment.

   (d) The provisions of this section shall not be amended by the Legislature except by statute passed in each house by rollcall vote entered in the journal, two-thirds of the membership concurring, or by a statute that becomes effective only when approved by the electors.

25.5. In any criminal proceeding in which a plea of not guilty by reason of insanity is entered, this defense shall not be found by the trier of fact solely on the basis of a personality or adjustment disorder, a seizure disorder, or an addiction to, or abuse of, intoxicating substances. This section shall apply only to persons who utilize this defense on or after the operative date of the section.

 

References:
California Penal Code