PART III. – BASIC PRINCIPLES OF GOVERNMENT.
Division 3. – Basic Rights.
Subdivision B. – Fundamental Rights.
37. PROTECTION OF THE LAW.
(7) No person shall be convicted of an offence on account of any act that did not, at the time when it took place, constitute an offence, and no penalty shall be imposed for an offence that is more severe in degree or description than the maximum penalty that might have been imposed for the offence at the time when it was committed.
Non-retroactivity
Nullum crimen sine lege
EDIT.