Decl. of Rights, Art. XXIV
No ex post facto laws
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Criminal Justice
Declaration of Rights
Official text rightpowerlimitif conditionlegal term
Laws made to punish for actions done before the existence of such laws, and which have not been declared crimes by preceding laws, are unjust, oppressive, and inconsistent with the fundamental principles of a free government.
Simplified explanation
Laws that punish actions done before those laws existed, and that were not declared crimes by earlier laws, are unjust, oppressive and inconsistent with the fundamental principles of a free government.