CHAPTER 3
FUNDAMENTAL HUMAN RIGHTS AND FREEDOMS
Article 12
Fair Trial
(3) No persons shall be tried or convicted for any criminal offence or on account of any act or omission which did not constitute a criminal offence at the time when it was committed, nor shall a penalty be imposed exceeding that which was applicable at the time when the offence was committed.
Non-retroactivity
Nullum crimen sine lege
EDIT.