ABSTRACT
An ex post facto law is one that punishes individuals for acts that were not criminal when they were committed or that enhances penalties for crimes previously committed. This was an injustice the founding fathers of the United States associated with the government of Great Britain and hoped to prevent. In Calder v. Bull, 3 US 386, the US Supreme Court set out several categories of laws that would violate the Ex Post Facto Clause of the Constitution. The Supreme Court set out a two-part test in Weaver v. Graham, 450 US 24, clarifying that an ex post facto violation can exist only when the law is applied retroactively and when the change in the law has been substantive rather then procedural. In Lynce v. Mathis, 519 US 433, the US Supreme Court found an ex post facto violation when a prisoner challenged a state statute that had retroactively canceled his provisional early release credits.
