ex post facto ex post facto

I believe it's "ex post facto."

Ex post facto law

I think you mean ex post facto, which is latin for "after the fact" I think you mean ex post facto, which is latin for "after the fact"

The legal term for a law that has criminal penalties that effect people prior to the enactment of that law is called an "ex-post facto law". Ex-post facto laws are illegal in most countries and the US Constitution expressly forbids the creation or passage of an ex-post facto law.