War crime

War crimes are, generally, acts that violated the laws of war that applied in the jurisdiction and time of occurrence. That being said, there is abundant precedent for the trial and conviction of defendants in an ad hoc tribunal that enforced issues ex post facto, because the offense had not been considered prewar, but, such as genocide, met a consensus of qualifying as egregious conduct, perhaps under the doctrine of hostis humani generis or of just war theory.

In the present international environment, the most important definitions are in the Geneva Conventions. There are complex issues when dealing with national decisions, such as the doctrine of command responsibility stated in the in re Yamashita decision. International law has generally not stayed abreast of non-state actors accused of terrorism or genocide, democide, or "ethnic cleansing".

Not all those individuals accused of war crimes have come to trial. Adolf Hitler, Joseph Goebbels and Heinrich Himmler all committed suicide before any legal process, and were not tried in absentia as was Martin Bormann. "War criminal" has become a term of art for those for whom there was abundant evidence, often in sworn testimony, but were never formally prosecuted due to their death or, as in the case of Josef Mengele, escape.

Aftermath of WWII

Post-WWII tribunals at Nuremberg and Tokyo did rule ex post facto in matters such as crimes against peace, although there was some legal background such as the Kellogg-Briand Pact and the Hague Conventions; see Article 19 in the Charter below

The Charter of the International Military Tribunal (Nuremberg), conducted the only four-power trial, operated under a charter that said"

• Crimes to be tried
  • (a) CRIMES AGAINST PEACE: namely, planning, preparation, initiation or waging of a war of aggression, or a war in violation of international treaties, agreements or assurances, or participation in a common plan or conspiracy for the accomplishment of any of the foregoing;
  • (b) WAR CRIMES: namely, violations of the laws or customs of war. Such violations shall include, but not be limited to, murder, ill-treatment or deportation to slave labor or for any other purpose of civilian population of or in occupied territory, murder or ill-treatment of prisoners of war or persons on the seas, killing of hostages, plunder of public or private property, wanton destruction of cities, towns or villages, or devastation not justified by military necessity;
  • (c)CRIMES AGAINST HUMANITY: namely, murder, extermination, enslavement, deportation, and other inhumane acts committed against any civilian population, before or during the war; or persecutions on political, racial or religious grounds in execution of or in connection with any crime within the jurisdiction of the Tribunal, whether or not in violation of the domestic law of the country where perpetrated.
• Article 19: The Tribunal shall not be bound by technical rules of evidence. It shall adopt and apply to the greatest possible extent expeditious and nontechnical procedure, and shall admit any evidence which it deems to be of probative value.
• Article 21: The Tribunal shall not require proof of facts of common knowledge but shall take judicial notice thereof. It shall also take judicial notice of official governmental documents and reports of the United Nations, including the acts and documents of the committees set up in the various allied countries for the investigation of war crimes, and of records and findings of military or other Tribunals of any of the United Nations.

The IMT proper conducted only one trial, called "International Military Tribunal for the Trial of German Major War Criminals." Note that "alleged" or similar qualifiers were not used. Subsequently, the four major powers conducted trials under their national authorities, such as U.S. Nuremberg Military Tribunals

International Criminal Court

The International Criminal Court has " jurisdiction over genocide, crimes against humanity and war crimes. These crimes are defined in detail in the Rome Statute. In addition, a supplementary text of the “Elements of Crimes” provides a breakdown of the elements of each crime. " Its jurisdiction applies to both the direct perpetrators "as well as others who may be liable for the crimes, for example by aiding, abetting or otherwise assisting in the commission of a crime. The latter group also includes military commanders or other superiors whose responsibility is defined in the Statute."

U.S. law

U.S. law defines war crimes principally in terms of the Geneva Conventions. The statute does not address the requirements of trial and conviction. "war crime” means any conduct—

1. defined as a grave breach in any of the international conventions signed at Geneva 12 August 1949, or any protocol to such convention to which the United States is a party;
2. prohibited by Article 23, 25, 27, or 28 of the Annex to the Hague Convention IV, Respecting the Laws and Customs of War on Land, signed 18 October 1907;
3. which constitutes a grave breach of common Article 3 (as defined in subsection (d)) when committed in the context of and in association with an armed conflict not of an international character; or
4. of a person who, in relation to an armed conflict and contrary to the provisions of the Protocol on Prohibitions or Restrictions on the Use of Mines, Booby-Traps and Other Devices as amended at Geneva on 3 May 1996 (Protocol II as amended on 3 May 1996), when the United States is a party to such Protocol, willfully kills or causes serious injury to civilians.