A criminal law may be changed owing to various reasons. Obsoleteness, loopholes and insufficiency of penalties on the part of the existing criminal law are some of the justifications which may warrant its amendment or replacement. Even though changing a criminal law following changes in circumstances is vital and advisable, the advent of a new criminal law may create the difficulty of determining the temporal scope of application of the former and the new laws. An interesting solution for such problem is the principle of nonretroactivity of criminal law, which states that a criminal law is applicable only to offences committed subsequent to its enactment. Nevertheless, this principle has some exceptions, which allow the retrospective application of a criminal law.
The purpose of this article is, therefore, to explicate the meanings of and justifications for the (non) retroactivity of criminal law, to show how they are incorporated and how they must be comprehended under Ethiopian criminal law.
2. (Non)retroactivity of Criminal Law
The word “retroactive” denotes “extending in scope or effect to matters that have occurred in the past”. It follows that retroactive legislation, also known as ex post facto laws, are “[l]aws which, expressly or by implication, operate so as to affect acts done prior to their having been passed.” In the context of criminal law, retroactivity is “to make an action a crime that was not a crime at the time it was done.” As such, retroactivity of criminal law “means that even a person well-informed about the law will be ignorant of the illegality of her or his acts because those acts are not deemed illegal until the retroactive law is made.” Conversely, the notion of nonretroactivity of criminal law suggests that criminal law should be applicable only to crimes done after the coming into force of the law.