Chapter II
Fundamental Rights, Freedoms and Duties
ยง 23.
No one may be convicted of an act which did not constitute a criminal offence under the law in force at the time the act was committed.
No one may be sentenced to a penalty that is more severe than the one that was applicable at the time the offence was committed. If, subsequent to the commission of the offence, the law makes provision for a lighter penalty, the lighter penalty applies.
EDIT.