Ex Post Facto Laws

Ex Post Facto Laws

An ex post facto law is a law that provides for punishment for an act that was committed when the act was not illegal. Additionally, an ex post facto law includes:

  • a law that makes an act more severe in nature than when it was committed
  • a law that imposes a harsher sentence for the offense than when it was committed
  • a law that changes the rules of evidence, thereby requiring less or more evidence at trial
  • a law that deprives the defendant of some protection that was previously offered

An ex post facto law is prohibited under the federal and most state constitutions. An ex post facto law is prohibited for two reasons. The first reason is to prevent legislatures from enacting arbitrary or vindictive legislation. The second reason is to assure that legislative acts give proper warning as to their effect.

When a Law Constitutes an Ex Post Facto Violation

A law is considered an ex post facto violation when:

  • the law is retrospective or applies to an offense or event that occurred before the enactment of the law
  • the law is a penal statute, which causes the defendant to be disadvantaged.

When a law is applied to a continuing offense that is in progress at the time that the new law becomes effective, no ex post facto violation has occurred. However, where a new law is applied to a continuing offense, the defendant must be afforded an opportunity to avoid liability by terminating his criminal conduct within a reasonable time after the passage of the new law. A change to a law that is procedural in nature does not constitute an ex post facto violation.

When the New Law Disadvantages the Defendant

To determine whether the new law may disadvantage the defendant, one must first determine whether the legislature intended the law to further punitive goals or to deter future offenses. If the legislative intent is not punitive, the defendant must show that the law is punitive in nature.

If the law creates a new crime or broadens the definition of an existing one, the law is punitive. Furthermore, if a new law creates an enhanced penalty for an existing offense, the new law may not be retroactively applied to the defendant. If a new law creates a mandatory minimum sentence, that law may not be applied to the defendant.


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