PART II
FUNDAMENTAL RIGHTS, DUTIES, LIBERTIES AND GUARANTEES
TITLE II
PERSONAL RIGHTS, FREEDOMS AND GUARANTEES
Section 31 (Application of criminal law)
2. No one shall be tried and convicted for an act that does not qualify in the law as a criminal offence at the moment it was committed, nor endure security measures the provisions of which are not clearly established in previous law.
EDIT.