The question of a defendant’s sanity is irrelevant at the guilt phase of a bifurcated trial under Penal Code section 1026 and, as a result, the court should not instruct the jury on the subject. Mills was charged with murder. He pleaded not guilty and raised an insanity defense. During the guilt phase trial, the defense presented evidence of Mills’ mental illness in an attempt to prove “imperfect” self-defense. Over defense objection, the trial court instructed the jury that Mills was conclusively presumed to have been sane at the time of the offense. In his appeal from his subsequent murder conviction, Mills contended that the guilt phase instruction on the conclusive presumption of sanity was improper because (1) it told the jury to presume the existence of a mental state critical to the state’s burden of proof, violating due process, and (2) it had no application to any issue before the jury, violating state law. The Court of Appeal affirmed. On review, the California Supreme Court found no due process error. The jury was instructed on the relationship between the evidence of mental illness and the intent elements of murder, and that they must decide whether Mills had the requisite mental state. The manner in which the case was tried left no reasonable likelihood that the jury applied the presumption of sanity to reduce the prosecution’s burden of proof. The jury was likely to conclude that the presumption operated to preserve the issue of sanity for the appropriate phase. The instruction was improper under state law, however, because it was irrelevant to any issue raised by the guilt phase evidence. The purpose of bifurcation is to remove entirely from the first stage of the trial any issue as to legal sanity. The defendant is presumed to be sane for procedural purposes, not for any evidentiary purpose. The instruction on presumption of sanity complicated matters by injecting the subject of sanity before it was at issue. However, Mills was not prejudiced by the improper instruction under the facts of this case.