CONSTITUTION OF THE REPUBLIC OF CROATIA
III. PROTECTION OF HUMAN RIGHTS AND FUNDAMENTAL FREEDOMS
2. PERSONAL AND POLITICAL LIBERTIES AND RIGHTS
Article 31
No one may be punished for an act which, prior to its commission, was not defined as a punishable offence by domestic or international law, nor may such individual be sentenced to a penalty which was not then defined by law. If a less severe penalty is determined by law after the commission of said act, such penalty shall be imposed.
Nullum crimen sine lege
Nulla poena sine lege
EDIT.