PART TWO
Individual and Social Rights
Article 7
1. There shall be no crime, nor shall puni-shment be inflicted unless specified by law in force prior to the perpetration of the act, defin¬ing the constitutive elements of the act. In no case shall punishment more severe than that specified at the time of the perpetration of the act be inflicted.
Non-retroactivity
Nullum crimen sine lege
Nulla poena sine lege
EDIT.