In PA in order to find the Defendant not guilty by reason of legal insanity, you must be satisfied beyond a reasonable doubt that he committed the otherwise criminal act charged, and you must also be satisfied by a preponderance of the evidence; first, that at the time of the act the Defendant had a mental disease or defect; and, second, that as a result of that disease or defect the Defendant was either incapable of knowing what he was doing, or if he did know, he was incapable of knowing that it was wrong. The Commonwealth notes that this Court addressed the issue of the burden of proof required by Sections 314 and 315 of the Crimes Code in Sohmer, where it was recognized that a defendant's sanity is presumed, see Sohmer, 519 Pa. at 208 n. 3, 546 A.2d at 605 n. 3; that the burden of establishing insanity, by a preponderance of the evidence, is on the defendant, see id.; and, further, that neither the defendant nor the Commonwealth has the burden of establishing mental illness, because that was a factual determination to be made from the evidence as a whole. See id. at 212, 546 A.2d at 607. The Commonwealth contends that the Legislature has made a policy judgment that a finding of guilt with mental illness does not negate the intent element of crimes, nor should it act as a mitigating factor at sentencing. See Commonwealth v. Morris, 385 Pa.Super. 563, 561 A.2d 1236 (1989); 42 Pa.C.S. § 9727. We will not convict a defendant who, at the time he committed an otherwise criminal act, was "laboring under such defect of reason, from disease of mind, as not to know the nature and quality of the act he was doing; or, if he did wrong, that he did not know he was doing wrong...." The Queen v. M'Naghten, 10 Cl. & Fin. 200, 8 Eng. Rep. 718 (1843); Commonwealth v. Woodhouse, 401 Pa. 242, 164 A.2d 98 (1960). To the extent we focus on the disorder to excuse the act, etiology is irrelevant. Commonwealth v. Simms, 462 Pa. 26, 333 A.2d 477 (1975) (insanity defense allowed where defendant, at the time of the crime, was allegedly acting as a result of a blow or blows to the head); Commonwealth v. Hicks, 483 Pa. at 311 n. 5, 396 A.2d at 1186 n. 5 (the Court reserved the question of "the applicability of the defense of insanity where the mental disease is traceable to habitual long term abuse of drugs.").
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