(dissenting in part, with whom Kaplan, J., joins). As in the recent case of Commonwealth v. Kostka, ante, 516 (1976), I am impelled to utilize the unusual procedure of writing the main opinion for the court and including in this separate opinion my dissent from the court’s reasoning in declining to set aside the verdict in this case under § 33E.
Once again we are faced on appeal with a case in which there was uncontradicted expert testimony that the defendant — who had a long history of mental disease antedating the crime — was insane at the time he committed the offenses with which he was charged. In my opinion, not only is the fact that the Commonwealth has chosen not to produce affirmative evidence of sanity “inexplicable” (see People v. Silver, 33 N.Y.2d 475, 483 [1974]), but it results, in this case, in injustice of the kind this court may prevent by exercising our discretion under § 33E.
In the majority’s refusal to act under § 33E here, I discern a trend toward treating the Commonwealth’s burden on the sanity issue in cases like Commonwealth v. Mutina, 366 Mass. 810 (1975), and Commonwealth v. Cox, 327 Mass. 609 (1951), differently from its burden in cases such as this one and Commonwealth v. Kostka, supra. There may be some validity to this trend; but the problem remains as to just what role the “presumption of sanity” should play in these cases. I suggest that a more uniform approach by this court would place the Commonwealth on notice that the failure to introduce medical evidence of sanity, in the face of credible evidence tending to establish insanity, means that the Commonwealth “runs the very real risk of reversal and the granting of a new trial” under the provisions of § 33E. Commonwealth v. Kostka, supra at 539-540, (Hennessey, C.J., and Kaplan, J., dissenting in part).