An “ex post facto” law-this is latin for after the deed and is sometimes referred to as a retrospective law.
it protects an individual from being charged with a crime that was not considered a crime when the act was committed.
article 1, section 9, clause 3: no ...........ex post facto law shall be passed. opposition to ex post facto laws was a bedrock principle among the framers. in the federalist no 78 alexander hamilton noted that the subjecting of men to punishment for things which they were done, were breaches of no law is among the favorite and most formidable instruments of tyranny thomas jefferson said ex post facto laws are against natural right.