Also known as: ex post facto law · ex-post-facto law · ex-post-facto laws · ex post facto · ex-post-facto
Written by attorneys · grounded in primary & secondary sources — see below
A constitutional prohibition that bars the federal government and the states from enacting legislation making conduct criminal that was lawful when performed, increasing the punishment for a completed offense, or altering rules of evidence to make conviction easier.
Evelyn Ellison raised rents on her apartment buildings four years before any statute addressed the practice. After Franklin enacted a new felony for prior rent increases above a threshold, prosecutors charged her using old lease records. The court dismissed the charges because the statute retroactively criminalized conduct lawful when performed.
Eileen Epstein completed a financial transaction that became time-barred under the original statute of limitations. A later statute extended the period and prosecutors sought to charge her for the old conduct. The court rejected the indictment because the extension reopened punishment for completed acts after the bar had run.
Select any source to read its text and confirm it supports the definition.
Eduardo Enriquez acquired cultural artifacts decades earlier under rules then in force. Congress later made such past acquisitions a federal crime and prosecutors indicted him. The court dismissed the charges because the statute retroactively attached criminal liability to lawful prior conduct.
Emma Erickson was convicted of trafficking under penalties in effect at the time of her offense. A new statute raised mandatory minimums and directed their application to all prior offenses. The sentencing court refused to impose the higher terms because they would increase punishment for completed conduct.
Enzo Eastwood completed his offense before a sex-offender registration statute took effect. Officials sought to impose the registration and notification requirements on him. The court upheld the measure because it was civil and regulatory rather than punitive in purpose and effect.
Ethan Evans committed his crime under a prior capital sentencing scheme later invalidated. A new statute replaced it with procedures that did not increase the likelihood of death. The court applied the new procedures because they altered only process without raising the quantum of punishment.
The clause prohibits legislation that retroactively makes conduct criminal which was lawful when performed, increases punishment for a completed offense, or changes rules of evidence to the defendant's disadvantage.
Supporting sources
Yes. Article I Section 9 bars Congress and Article I Section 10 bars the states from passing ex post facto laws.
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Yes. Extending a statute of limitations after it has expired and applying it to past conduct violates the clause by retroactively altering the quantum of evidence needed for conviction.
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Yes. A statute that raises maximum or mandatory minimum sentences and applies them to offenses committed before its enactment increases punishment for past conduct and is invalid.
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Only if they are so punitive in purpose or effect that they function as criminal punishment. Otherwise civil registration or notification schemes may apply to prior offenses.
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No, but due process forbids courts from retroactively interpreting criminal law in an unexpected and indefensible way that disadvantages defendants.
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…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…