Commonwealth v. McCusker

Opinion by

Me. Justice Roberts,

We must decide today whether psychiatric evidence is admissible in a murder prosecution for the limited purpose of determining whether a defendant acted in the heat of passion. We are persuaded by the almost unanimous voice of professionally recognized authorities1 that such evidence is competent and in certain circumstances admissible. Appellant did not raise the defense of complete insanity. Our decision today does not in any manner affect the M’Naghten test presently em*385ployed in this Commonwealth to determine a defendant’s sanity. Commonwealth v. Melton, 406…