Under the principle of legality, laws, which hold a person legally responsible for acts committed before the law was passed, are not binding.

ex post facto

Explanation:

Under the principle of legality, ex post facto laws, which hold a person legally responsible for acts committed before the law was passed, are not binding.  

The principle of legality states that an individual cannot be convicted for a crime that has not be publicly announced, recognized as a crime by the public or the law at the time the action was committed.  Thus, ex post facto laws which holds an individual responsible for a crime that was committed when that action had not yet been criminalized is over ruled by the principle of legality.

answerdavid strayer;