4. No person shall be liable to be tried or punished in any court in Nigeria for an offence,
except under the express provisions of the code or of some Act or Law which is in force in, or forms part of the law of Nigeria :
Provided that in the case of an offence committed before the commencement of this Act the
offender may be tried and punished either under the law in force when the offence was committed or under the code, provided that the offender shall not be punished to any greater extent than was authorised by the former law.

Article 23
Nulla poena sine lege
A person convicted by the Court may be punished only in accordance with this Statute.