In Mullaney v. Wilbur, 1974, the U.S. Supreme Court ruled that it was unconstitutional for a state to require defendants in murder cases to prove they acted "in the heat of passion on sudden provocation" in order to reduce their charge from murder to manslaughter. The case involved a Maine law which placed this burden of proof on defendants rather than prosecutors. The court held that this violated the Due Process Clause of the Fourteenth Amendment because it effectively presumed guilt without requiring the prosecution to prove every element of the crime beyond reasonable doubt - one such element being malice aforethought, which distinguishes murder from manslaughter under common law principles. This decision reinforced and clarified previous rulings asserting that due process requires states must bear all burdens related to proving criminal charges.

In the dissenting opinion for Mullaney v. Wilbur, Justice William Rehnquist argued that the majority's decision was a departure from established precedent and an intrusion into state lawmaking authority. He contended that it is not within the Court’s purview to dictate how states should allocate burdens of proof in their criminal laws. The majority ruling required Maine to prove beyond reasonable doubt all elements of a crime including absence of heat-of-passion on sudden provocation, which traditionally had been considered as mitigating factors rather than elements of crimes themselves. This shift, according to Rehnquist, would have far-reaching implications for many other states with similar legal structures and could potentially disrupt their entire criminal justice systems.