COOK ISLANDS – CONSTITUTION
PART IVA - FUNDAMENTAL HUMAN RIGHTS AND FREEDOMS
Construction of law
65 (1) Subject to subclause (2) of this Article and to subclause (2) of Article 64 hereof, every enactment shall be so construed and applied as not to abrogate, abridge, or infringe or to authorise the abrogation, abridgement, or infringement of any of the rights or freedoms recognised and declared by subclause (1) of Article 64 hereof, and in particular no enactment shall be construed or applied so as to-
(g) Authorise the conviction of any person of any offence except for the breach of a law in force at the time of the act or omission;
Non-retroactivity
Nullum crimen sine lege
EDIT.