''Title III, The Fundamental Freedoms and Rights, Art 20''
The penal laws cannot have retroactive effect.
2. If a State becomes a Party to this Statute after its entry into force, the Court may exercise its jurisdiction only with respect to crimes committed after the entry into force of this Statute for that State, unless that State has made a declaration under article 12, paragraph 3.
1. No person shall be criminally responsible under this Statute for conduct prior to the entry into force of the Statute.
2. In the event of a change in the law applicable to a given case prior to a final judgement, the law more favourable to the person being investigated, prosecuted or convicted shall apply.