Imagine being arrested for something that *wasn't* illegal when you did it! That's the chilling reality ex post facto laws prevent. Derived from Latin meaning "from after the action," these laws are forbidden under the U.S. Constitution. They essentially do three things, all considered unjust:
1. Criminalize actions that were legal when committed.
2. Increase the punishment for a crime *after* it was committed.
3. Alter the rules of evidence to make conviction easier *after* the fact.
Think of it this way: If you legally purchased fireworks last July, a new law passed in August can't suddenly make your past purchase a crime and subject you to a fine. Ex post facto laws are designed to protect individuals from arbitrary and unfair applications of the law, ensuring fairness and predictability in the legal system. They safeguard against retroactive justice, which is crucial for a stable society.
