Under federal law, murder is defined as "the unlawful killing of a human being with malice aforethought." 18 U.S.C. § 1. Voluntary manslaughter is defined as "the unlawful killing of a human being without malice[, u]pon a sudden quarrel or heat of passion." 18 U.S.C. § 1112(a).

In Mullaney v. Wilbur, 421 U.S. 684, 692-704 (1975), after examining the historical development of homicide crimes, this Court held that Due Process requires the prosecution to prove the absence of the heat of passion in order to convict a defendant of murder, when the evidence would also support a jury's conclusion that the defendant acted in the heat of passion.

The question presented here is: In a federal homicide prosecution, must the jury be instructed that the government has the burden of proving the absence of the heat of passion before the jury can find a defendant guilty of second degree murder whenever a party requests that the jury consider the lesser included offense of voluntary manslaughter? Or is such an instruction only required when the defendant argues for or requests instruction on the lesser included offense?

Must the jury be instructed that the government has the burden of proving the absence of the heat of passion before finding a defendant guilty of second degree murder when a lesser included offense of voluntary manslaughter is considered?