Also known as: ex post facto violations · ex-post-facto violation · ex post facto law violation · ex post facto · ex post facto law
Written by attorneys · grounded in primary & secondary sources — see below
A constitutional prohibition barring legislatures from enacting criminal laws that operate retroactively to the disadvantage of the accused. The bar covers statutes that criminalize conduct lawful when performed, increase punishment for completed offenses, or alter evidentiary rules to make conviction easier.
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Eduardo Enriquez managed a waste facility in State Green. Years earlier his disposal practices complied fully with then-existing environmental rules. A new state statute reclassifies those same past methods as felonies and directs prosecutors to charge based on archived compliance reports. The court dismisses the charges because the statute retroactively imposes criminal liability for previously lawful conduct.
Eva Espinosa was investigated for securities fraud in 2015. The five-year limitations period expired without charges. In 2022 Congress enacts a statute extending the period to ten years and expressly reviving expired cases. Prosecutors indict her under the new law. The court dismisses the indictment because the extension retroactively reopens punishment for conduct whose prosecution had already become impossible.
Evergreen Bank financed industrial projects whose emissions exceeded newly adopted federal ceilings during the prior decade. No ceilings existed at the time of the projects. Congress passes the Carbon Accountability Act making such past exceedances federal crimes. Prosecutors charge the bank under the Act. The court dismisses the case because the statute retroactively criminalizes conduct lawful when undertaken.
Esme Ellington inherited copyrights in works published in 1925. Congress extends the term by twenty years after the works entered the public domain. Esme sues a publisher for infringement based on the extended term. The court upholds the extension because the change affects only civil remedies and does not impose or increase criminal punishment.
Emma Erickson sold materials in 1970 that met the prevailing obscenity test at the time. A later Supreme Court decision adopts a new community-standards test that would classify the same materials as obscene. Prosecutors attempt to apply the new test to the 1970 sales. The court rejects the prosecution because the retroactive change in substantive criminal law would violate the prohibition on ex post facto punishment.
Esther Eisenberg held title to enslaved persons under state law in 1856. A later federal statute declares all such holdings unlawful and imposes criminal penalties for prior ownership. Prosecutors bring charges based on the 1856 conduct. The court dismisses the indictment because the statute retroactively criminalizes conduct that was lawful when performed.
A statute violates the prohibition when it retroactively makes previously lawful conduct criminal, increases the punishment attached to a completed offense, or alters rules of evidence to make conviction easier. The constitutional bar protects fair notice by preventing legislatures from changing the legal consequences of past acts after the fact.
Supporting sources
The clause applies only to criminal laws. Civil regulatory measures, even when retroactive, do not violate the prohibition unless they are so punitive in purpose or effect that they function as criminal punishment.
…a measure was "necessary and proper" to the discharge of its substantive legislative authority, pass a bill of attainder or ex post facto law contrary to the prohibitions contained in § 9 of Art. I. No more may it vest in itself, or in its officers, the authority to appoint officers of the United States when the Appointments…
…The Court rested the invalidation on alternative sources of authority: the specific prohibitions against bills of attainder, ex post facto laws, laws impairing contracts in Article I, § 10, of the Constitution; and "general principles which are common to our free institutions," by which Chief Justice Marshall meant that a…
…321. [^maj-12]: The significance of this pronouncement cannot be minimized. The holding that retrial by a jury of eight was an ex post facto law is perforce built upon the conclusion that the jury of 12 was a right of substance. If the right were merely a procedure mandated by statute, it would not have required the ex
…Money; emit Bills of Credit; make any Thing but gold or silver Coin a Tender in Payment of Debts; pass any Bill of Attainder, ex post facto Law
…supra , at 648. For I am unwilling to assume what appellants made no effort to prove, that the possibility of obtaining an
Supporting sources
No. Extending a statute of limitations after it has already expired and applying the extension to previously time-barred conduct violates the clause because it reopens the possibility of punishment for acts whose prosecution had become impossible.
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A procedural change that does not increase the quantum of punishment is generally permissible. Only changes that retroactively increase the penalty or alter the substantive elements of the offense trigger the prohibition.
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The clause itself constrains only legislatures. Due process nevertheless forbids courts from applying an unexpected and indefensible retroactive interpretation of criminal law that disadvantages the defendant.
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