Chapter IV
Fundamental Rights
36. (8) No person shall be held to be guilty of a criminal offence on account of any act or omission that did not, at the time it took place, constitute such an offence, and no penalty shall be imposed for any criminal offence heavier than the penalty in force at the time the offence was committed.
Non-retroactivity
Nullum crimen sine lege
Nulla poena sine lege
EDIT.