A law that makes illegal an act that was legal when committed, increases the penalties for an infraction after it has been committed, or changes the rules of evidence to make conviction easier. The Constitution prohibits the making of ex post facto law. (See ex post facto.)
ex post facto law
law that retroactively makes criminal conduct that was not criminal when performed, increases the punishment for crimes already committed, or changes the rules of procedure in force at the time an alleged crime was committed in a way substantially disadvantageous to the accused.
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