In Mullaney v. Wilbur (1975) 421 U.S. 684, the California Supreme Court invalidated a Maine law that put the burden on the defendant to prove the defendant acted in the heat of passion in order to reduce a charge of murder to manslaughter. The court held that the law violated the due process requirement that the prosecution prove the defendant's guilt beyond a reasonable doubt. Mullaney v. Wilbur does not hold, as defendants claim, that in any case in which a defendant is charged with murder the prosecution must prove the absence of heat of passion in order to prove the defendant acted with malice aforethought. In fact, as defendants note, the Supreme Court expressly stated, "Many states do require the defendant to show that there is 'some evidence' indicating that he acted in the heat of passion before requiring the prosecution to negate this element by proving the absence of passion beyond a reasonable doubt. Nothing in this opinion is intended to affect that requirement." (Mullaney v. Wilbur, supra, 421 U.S. at p. 701 fn. 28.)