Ex post facto law
An ex post facto law is a law that retrospectively changes the legal consequences or status of actions that were committed, or relationships that existed, before the enactment of the law. In criminal law, it may criminalize actions that were legal when committed; it may aggravate a crime by bringing it into a more severe category than it was in when it was committed; it may change the punishment prescribed for a crime, as by adding new penalties or extending sentences; it may extend the statute of limitations; or it may alter the rules of evidence in order to make conviction for a crime likelier than it would have been when the deed was committed.