Respuesta :
A law that makes illegal an act that was legal when committed, hope this helps.
Answer:
An ex post facto law is a law that punishes an action retroactively even if the action was not considered illegal by the time it took place. It can also increase the penalty of an action already judged. The U.S. Constitution prohibits the Congress and States to pass ex post facto laws under the principle that one must be judged according to the laws valid before the action took place, not after.
