Practice Relating to Rule 158. Prosecution of War Crimes
New Zealand’s Military Manual (1992) states:
The [1949 Geneva] Conventions make one further departure of significance. For the first time they provide in treaty form a clear obligation upon States to punish what the Conventions describe as “grave breaches”, even if those States are not parties to the conflict, the offenders and the victims not their nationals, and even though the offences were committed outside the territorial jurisdiction of the State concerned. In other words, the Conventions have introduced the concept of universal jurisdiction in so far as grave breaches are concerned, and if the State in question is unwilling to try an offender found within its territory, it is obliged to hand him over for trial to any party to the Convention making out a prima facie
The manual also notes:
In the event of “any alleged violations” of the 1949 [Geneva] Conventions an enquiry must be instituted at the request of a Party to the conflict. If a violation be established, the Parties to the conflict must put an end to it and punish it with the least possible delay.
The manual further provides:
The four  Geneva Conventions require the parties to them to enact such legislation as may be necessary to provide effective sanctions for persons committing or ordering any of the acts which would constitute grave breaches under the Conventions. They also provide that the parties will take the measures necessary to suppress any violation of the Convention[s] not amounting to grave breaches.
The manual adds: “Any grave breach described as such in the [1949 Geneva] Conventions and [the 1977 Additional Protocol I] shall be an indictable offence.”
New Zealand’s Geneva Conventions Act (1958), as amended in 1987, provides:
(1) Any person who in New Zealand or elsewhere commits, or aids or abets or procures the commission by another person of, a grave breach of any of the [1949 Geneva] Conventions or of the First [Additional] Protocol is guilty of an indictable offence.
(3) This section applies to persons regardless of their nationality or citizenship.
New Zealand’s International Crimes and ICC Act (2000) provides: “Every person is liable on conviction on indictment to the penalty specified in subsection (3) who, in New Zealand or elsewhere, commits a war crime.” The Act includes similar provisions with respect to genocide and crimes against humanity. War crimes, genocide and crimes against humanity are defined as the acts specified in the 1998 ICC Statute.
In 2009, in a statement before the UN General Assembly, in explanation of New Zealand’s voting abstention on the follow-up to the report of the United Nations Fact Finding Mission on the Gaza Conflict, the permanent representative of New Zealand stated: “New Zealand has consistently called for investigations into alleged violations of human rights and humanitarian law arising from the Gaza conflict. There should be no impunity. Perpetrators of any such violations must be brought to justice.”