WHAT IS AN EX POST FACTO LAW?
An ex post facto law is a law that is enacted to make an act illegal after it has been done. For example, Cecilia practices archery in the public park. Citizens get angry because they feel she is doing something dangerous. Citizens demand her arrest. The police say that they cannot do anything because there is no law against practicing archery in the park. Citizens vote to enact a law. Police then go to arrest Cecilia for breaking this “ex post facto” (“after the fact”) law before the law was enacted. Doesn’t seem fair, does it? Luckily, the United States Constitution bans ex post facto laws. Sure, citizens can vote to ban archery in the park. But the Constitution says Cecilia can’t be arrested for what she did before the law was enacted. The only way Cecilia can be arrested is if she practices archery in the park after the law against archery is enacted.
