Legal Definitions - ex post facto

Definition:Ex post facto is a Latin term that means "from a thing done afterward." It refers to a criminal statute that punishes actions retroactively, making conduct illegal that was legal when originally performed.

Examples:

• If a law is passed today that makes it illegal to drive a red car, and someone who drove a red car yesterday is punished for it, that would be an ex post facto law.
• If a person is convicted of a crime and sentenced to 10 years in prison, but then a new law is passed that increases the punishment for that crime to 20 years, the person cannot be retroactively sentenced to 20 years under the ex post facto clause.

These examples illustrate how ex post facto laws punish people for actions that were legal at the time they were performed or increase the punishment for a crime after it was committed. This violates the constitutionalprohibition against ex post facto laws.