William Rehnquist

“ It is possible to reconcile Kring with the numerous cases which have held that "procedural" changes do not result in ex post facto violations by saying that the change in Missouri law did take away a "defense" available to the defendant under the old procedure. But this use of the word "defense" carries a meaning quite different from that which appears in the quoted language from Beazell, where the term was linked to the prohibition on alterations in "the legal definition of the offense" or "the nature or amount of the punishment imposed for its commission." ”

“ The Beazell formulation is faithful to our best knowledge of the original understanding of the Ex Post Facto Clause: Legislatures may not retroactively alter the definition of crimes or increase the punishment for criminal acts. ”

“ This analysis is consistent with the Beazell framework. A law that abolishes an affirmative defense of justification or excuse contravenes Art. I, § 10, because it expands the scope of a criminal prohibition after the act is done. It appears, therefore, that Justice Washington's reference to laws "relat [ing] to the offence or its consequences," was simply shorthand for legal changes altering the definition of an offense or increasing a punishment. ”

“ Every law that alters the legal rules of evidence, and receives less, or different, testimony, than the law required at the time of the commission of the offence, in order to convict the offender." Id., at 390 (emphasis in original) . ”

“ Several early State Constitutions employed this definition of the term, and they appear to have been a basis for the Framers' understanding of the provision. See The Federalist No. 44, p. 301 (J. Cooke ed. 1961) (J. Madison) ; 2 M. Farrand, Records of the Federal Convention of 1787, p. 376 (1911) ; Calder, 3 Dall., at 391-392 (opinion of Chase, J.) ”