Also known as: prohibition of ex post facto law · ex post facto prohibition · ex post facto prohibitions · ex post facto clause · ban on retroactive laws
Written by attorneys · grounded in primary & secondary sources — see below
A constitutional prohibition that bars legislatures from enacting criminal laws that retroactively criminalize conduct lawful when performed, increase punishment for completed offenses, or alter rules of evidence to the defendant's disadvantage.
Parker Phillips completed a series of financial transactions in 1995. The applicable statute of limitations expired in 2000 without any charges filed. In 2003 Congress enacted a statute that revived the expired limitations period and authorized prosecution for those same transactions. Prosecutors then indicted Parker under the new statute.
Preston Pratt was convicted of an offense committed in 1997. At sentencing the court applied 2005 guidelines that raised the applicable range above the range in effect at the time of the offense. The higher range increased the minimum term Preston faced.
Select any source to read its text and confirm it supports the definition.
Pablo Perez completed a series of sexual offenses before Kansas enacted its Sexually Violent Predator Act. After release from prison the state sought to commit Pablo under the new statute based solely on those pre-enactment acts. The commitment proceeding turned on whether the statute imposed additional punishment for the earlier conduct.
It forbids retroactive criminal laws that make previously lawful conduct criminal, increase punishment for completed offenses, or change evidentiary rules to the defendant's disadvantage. The prohibition protects fair notice by ensuring individuals can rely on the law in effect when they act.
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No. The prohibition applies only to criminal punishment. Civil measures such as sex-offender registration remain valid 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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No. Extending a statute of limitations after it has already expired and applying the extension to past conduct violates the prohibition because it reopens the possibility of punishment for acts that could no longer be prosecuted.
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Yes. Applying a new statute or guideline that raises the maximum or mandatory minimum sentence to conduct completed before its enactment increases punishment after the fact and is therefore invalid.
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…of a mental condition. The Act therefore comports with due process. Pp. 356–360. 2. The Kansas Act does not violate the Ex Post Facto Clause . That Clause applies to criminal statutes. California Dept. of Corrections v. Morales , 514 U. S. 499, 504. The Kansas Act is civil, not criminal, in nature. The Court ordinarily…