Also known as: Ex Post Facto Clause · ex post facto law · ex post facto prohibition
Written by attorneys · grounded in primary & secondary sources — see below
A constitutional prohibition barring legislatures from enacting criminal laws that retroactively criminalize conduct lawful when performed, increase punishment for completed acts, or alter evidentiary rules to the defendant's disadvantage.
Eduardo Enriquez sold counterfeit goods in State A last year when the maximum sentence was five years. After a new statute raised the maximum to ten years and applied it to prior offenses, the state court imposed the higher term. The Ex Post Facto Clause blocks the increased punishment because the conduct occurred before the change.
Elise Everly completed an alleged offense in 1995 when the statute of limitations expired in 2000. A 2002 statute revived the prosecution by extending the period. The court dismisses the case because the new law retroactively alters the quantum of evidence sufficient to convict for past conduct.
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Emily Ellis acquired artifacts in 1990 under then-lawful export rules. A later federal statute makes those acquisitions a crime and prosecutors indict her. The Ex Post Facto Clause invalidates the application because the statute retroactively criminalizes conduct lawful when performed.
Eric Espinoza was convicted after a state supreme court abolished the year-and-a-day rule in homicide cases. The change applied to his earlier conduct. Due process permits the retroactive judicial ruling because it was reasonably foreseeable given evolving medical standards and widespread abandonment of the rule.
Ella Emerson committed a capital offense under an invalidated statute that still gave notice of the death penalty. A new capital sentencing statute applied at trial does not increase the likelihood of death. The Ex Post Facto Clause permits the procedural change because punishment is not increased.
Eva Espinosa completed a sex offense before a registration statute took effect. The law requires registration and public notification for prior offenders. The Ex Post Facto Clause does not bar application because the measure is civil and nonpunitive in intent and effect.
An ex post facto law retroactively makes conduct criminal that was lawful when performed, increases punishment for past conduct, or alters rules of evidence to make conviction easier. The prohibition protects fair notice so individuals may rely on existing law when ordering their affairs.
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The clause applies only to criminal punishment. Civil regulatory measures such as sex-offender registration are permissible even when applied to prior offenses unless the measure is so punitive in effect that it overrides the legislature's civil intent.
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The Ex Post Facto Clause targets retroactive changes in criminal liability or punishment. A bill of attainder prohibition prevents legislative punishment of identifiable individuals or groups without judicial trial. A statute creating a generally applicable offense may raise an ex post facto issue but not a bill of attainder issue.
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The Ex Post Facto Clause binds only legislatures. Due process nevertheless bars courts from retroactively interpreting criminal law in an unexpected and indefensible manner. A change is permissible when evolving standards make the new rule reasonably foreseeable.
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…of the same state may be defended on a state law making paper money a legal tender; a criminal indictment may be defended as an ex post facto law; and in such instances the state court must hear and determine the matter. This clause recognizes the inevitability of state courts incidentally taking cognizance of federal cases and…