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.

Chapter IV
Fundamental Rights

36. (12) Subject as otherwise provided by this Constitution, a person shall not be convicted of a criminal offence unless that offence is defined and the penalty therefor is prescribed in a written law, and in this subsection, a written law refers to an Act of the National Assembly or a Law of a State, any subsidiary legislation or instrument under the provisions of a law.

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.