Unreasonable self-defense is a form of mistake of fact and therefore has no application when the defendant’s belief in the need to defend himself is entirely delusional. Defendant, who was mentally ill, stabbed to death a woman at a bus stop. When charged, Elmore pleaded not guilty and not guilty by reason of insanity. At trial his request for instructions on unreasonable self-defense and hallucination was denied. After his conviction of first degree murder he withdrew his insanity defense. The Court of Appeal reversed for failing to instruct on hallucination, but rejected appellant’s argument that the trial court erred for failing to instruct on unreasonable self-defense. Appellant sought review. Held: Affirmed. Manslaughter is an unlawful killing without malice. The factors that may negate malice are heat of passion and unreasonable self-defense, which must be based on an actual but unreasonable belief. “A belief in the need for self-defense that is purely delusional is a paradigmatic example of legal insanity,” which is an issue that is reserved for a separate phase of trial. “[U]nreasonable self-defense is not premised on considerations of mental disorder.” It is based on a defendant’s assertion that he lacked malice because he acted based on an unreasonable mistake of fact, i.e., that he needed to defend himself against the peril of great bodily injury or death. Because the doctrine is “a species of mistake of fact” and requires an objective basis, it cannot be based on delusion.

Penal Code section 28, subdivision (a) does not provide support for an unreasonable self-defense claim based on delusion. Section 28, subdivision (a) allows evidence of mental disorder on the issue of whether the defendant actually formed a required specific intent, premeditated, or formed malice aforethought. It bars evidence of a defendant’s capacity to form a required mental state. When viewed in totality, the statutory scheme governing evidence of mental illness, as well as the legislative history of section 28, reflect it was not intended to allow a defendant to introduce evidence that his belief in the need for self-defense was based entirely on a mental disorder. Mental incapacity is determined by the M’Nahgten test for insanity (Pen. Code, § 25, subd. (b))—whether the defendant was unable either to understand the nature and quality of the criminal act, or to distinguish right from wrong when it was committed. A claim of unreasonable self-defense based solely on delusion constitutes a claim of insanity under the right/wrong prong of M’Naghten. Thus, defendant attempted to assert an insanity claim in the guilt phase of his trial. Relevant evidence of mental states short of insanity is admissible at the guilt phase to negate a requisite element or to show unreasonable self-defense based on mistake of fact. But defendants who contend they killed in self-defense because of a purely delusional perception of threat must reserve that claim for the sanity phase.