Nulla poena sine lege or nullum crimen, nulla poena sine praevia lege poenali - "No penalty without law" or "no crime, no punishment without a previous penal law". (1) One cannot be prosecuted for doing something that is not prohibited by law. (2) One cannot be prosecuted for doing something that was not prohibited by law at the time and place it was committed, notwithstanding laws made since that time. A form of prohibition on retroactive laws.⏎
Probatio vincit praesumptionem - Proof overcomes presumption.⏎
Non faciat malum, ut inde veniat bonum - "Not to do evil that good may come." Performing some illegal action is not excused by the fact that a positive result came therefrom. Often used to argue that some forms of expression, such as graffiti or pornographic films, cannot be given the protection of law (e.g. copyright) as they are or may be considered illegal or morally reprehensible.⏎
Nullum crimen, nulla poena sine praevia lege poenali - There can be neither crime nor punishment unless there is a penal law first.⏎