What is Ex Post Facto Law?

Ex post facto is Latin for ‘after the fact’. The ex post facto clause in the US Constitution prevents citizens from being retried for a crime after the punishment for that crime has been changed. So say, for example, I steal a bag of Swedish fish from my local supermarket and I’m caught, and under the current law, my fine is to pay for the bag of Swedish fish. But someone decides that this isn’t enough punishment, and next month, a law is passed that changes the penalty for my crime to having to pay for the bag plus doing ten days of jail time (which is so not worth a bag of Swedish fish, but that’s beside the point). Anyway, under the ex post facto clause, I can’t be retried and made to serve the jail time, since I was already punished before the new law was put into place.You can find more information here: