Ex post facto

Latin term meaning "after the fact." Refers especially to a lawthat makes punishable as a crime an act done before the passing of the law andthat was innocent when done. An ex post facto law is also one that makes acrime more serious than when it was committed, inflicts a greater punishment,or alters legal rules of evidence to require less or different testimony toconvict than the law required when the crime was committed. Such laws violateprovisions of the Constitution of the United States, which provide that neitherCongress nor any state shall pass an ex post facto law.