A law passed after the occurrence of a fact or commission of an act, which retrospectively changes the legal consequences or relation of such fact or deed. By article 1, section 10 of the U.S. Constitution, the states are forbidden to pass any ex post facto law.
The term “ex post facto” literally means “after the fact.” A law that does any of the following would be cosidered an ex post facto law and thus prohibited under the Constitution:
- criminalizes conduct that was not criminal at the time committed;
- imposes more severe criminal charges;
- imposes more severe penalties; or
- allows admission of evidence more likely to result in a conviction.