Stillman Wilbur, Jr. (defendant) was charged with murder after he fatally assaulted Claude Hebert in Hebert’s hotel room. At trial, Wilbur claimed he acted in the “heat of passion” and was provoked to attack Hebert after Hebert made sexual advances toward him. The Maine homicide statute required Wilbur to prove he acted in the “heat of passion on sudden provocation” in order to reduce the charge from murder to manslaughter. Wilbur offered no such evidence. Wilbur was convicted and he appealed. The Maine Supreme Judicial Court affirmed the conviction. Thereafter, Wilbur filed a petition in federal district court for a writ of habeas corpus against Mullaney, the warden of the prison where Wilbur was incarcerated. The district court granted the petition and held that the prosecution was required to prove Wilbur’s malice aforethought beyond a reasonable doubt and that it could not rely on a presumption of implied malice, which required the Wilbur to prove that he acted in the heat of passion on sudden provocation. The court of appeals affirmed. The U.S. Supreme Court granted certiorari to review.