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.

Part 1
Introductory
Interpretation: Application: General Principles

Chapter 3
Application of Criminal Law

11. A person shall not be punished for doing or omitting to do an act of unless the act or omission constituted an offence under the law in force when it occurred.

Article 22
Nullum crimen sine lege
1. A person shall not be criminally responsible under this Statute unless the conduct in question constitutes, at the time it takes place, a crime within the jurisdiction of the Court.
2. The definition of a crime shall be strictly construed and shall not be extended by analogy. In case of ambiguity, the definition shall be interpreted in favour of the person being investigated, prosecuted or convicted.
3. This article shall not affect the characterization of any conduct as criminal under international law independently of this Statute.