Related Rule
New Zealand
Practice Relating to Rule 101. The Principle of Legality
New Zealand’s Military Manual (1992) states: “No prisoner may be tried or punished for any offence which was not, at the time of its commission, forbidden by international law or the law of the Detaining Power.” 
New Zealand, Interim Law of Armed Conflict Manual, DM 112, New Zealand Defence Force, Headquarters, Directorate of Legal Services, Wellington, November 1992, § 932(2).
The manual further states: “No one shall be accused or convicted of a criminal offence on account of any act or commission which did not constitute a criminal offence under the national or international law to which he was subject at the time when it was committed.” 
New Zealand, Interim Law of Armed Conflict Manual, DM 112, New Zealand Defence Force, Headquarters, Directorate of Legal Services, Wellington, November 1992, § 1137(4)(c).
The manual also states: “The penal provisions enacted by the Occupying Power must not be retroactive.” 
New Zealand, Interim Law of Armed Conflict Manual, DM 112, New Zealand Defence Force, Headquarters, Directorate of Legal Services, Wellington, November 1992, § 1327(1)(a).
The manual further states: “No person may be tried for a war crime unless the act in question was an offence at the time of its commission.” 
New Zealand, Interim Law of Armed Conflict Manual, DM 112, New Zealand Defence Force, Headquarters, Directorate of Legal Services, Wellington, November 1992, § 1711(3).
With respect to non-international armed conflicts, the manuals states:
No one shall be guilty of an offence in respect of any act or omission which was not an offence at the time of commission, nor shall any punishment be more severe than was applicable at that time, although, if the punishment has been alleviated, the accused shall benefit accordingly. 
New Zealand, Interim Law of Armed Conflict Manual, DM 112, New Zealand Defence Force, Headquarters, Directorate of Legal Services, Wellington, November 1992, § 1815(2)(c).