TITLE II
RIGHTS AND DUTIES OF THE INDIVIDUAL
ARTICLE 17.
No one shall be condemned for actions or omissions which, at the moment when they were committed, did not constitute an infraction according to the national law. Likewise, he may not have a more severe penalty inflicted than that which was applicable at the time when the offense was committed.
Nullum crimen sine lege
Nulla poena sine lege
EDIT.