298. International humanitarian law also specifically incorporates the principle of legality, including in the Third Geneva Convention, the Fourth Geneva Convention and API.663 Additionally, this prohibition is a norm of customary international humanitarian law.664 299. Recognized law of war offences are listed in several international treaties and statutes, including the Geneva Conventions and API,665 the International Criminal Court’s (ICC) Rome Statute,666 and the statutes of the ICTY and the International Criminal Tribunal for Rwanda (ICTR).667 For instance, torture and ill-treatment, murder of protected persons, intentionally directing attacks against civilians, intentionally directing attacks against civilian objects, taking of hostages and pillaging are recognized war crimes. b. Domestic Standards 300. In 1866, the United States Supreme Court held that military commissions should not be used to try civilians unconnected to military service in a territory that was not under martial law or military occupation when regular civilian courts “are open and their process unobstructed”.668 In the case of Ex parte Quirin, the United States Supreme Court recognized that Congress had authorized the establishment of military commissions to try enemy belligerents for violations of the law of war.669 301. The purpose of Guantánamo military commissions is to try only alien “unprivileged enemy belligerents” for law of war violations and for “other offenses triable by military commissions”, including aiding the enemy and spying.670 MCAs 2006 and 2009 list and define a number of offences that may be tried by military commissions, including conspiracy, providing material support for terrorism, solicitation and murder in the violation of war.671 These offences must have been committed “in the context of and 663 Third Geneva Convention, Art. 99: “[n]o prisoner of war may be tried or sentenced for an act which is not forbidden by the law of the Detaining Power or by international law, in force at the time the said act was committed”; Fourth Geneva Convention, Art. 65: “[t]he penal provisions enacted by the Occupying Power shall not come into force before they have been published (…). The effect of these penal provisions shall not be retroactive”; Art. 67: “The courts shall apply only those provisions of law which were applicable prior to the offence”; API, Art. 75(4)(c): “[n]o one shall be accused or convicted of a criminal offence on account of any act or omission 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; nor shall a heavier penalty be imposed than that which was applicable at the time when the criminal offence was committed; if, after the commission of the offence, provision is made by law for the imposition of a lighter penalty, the offender shall benefit thereby.” 664 “Customary International Humanitarian Law, Rule 101: The Principle of Legality”, ICRC website, <http://www.icrc.org/customary-ihl/eng/docs/v1_rul_rule101>. 665 First Geneva Convention, Art. 50; Second Geneva Convention, Art. 5; Third Geneva Convention, Art. 130; Fourth Geneva Convention, Art. 147; API, Art. 85. 666 Rome Statute, Art. 8. 667 Updated Statute of the ICTY, as amended in 7 July 2009, Arts. 2-3, <http://www.icty.org/x/file/Legal%20Library/Statute/statute_sept09_en.pdf>; Statute of the ICTR, 8 November 1993, Art. 4, <http://www.ohchr.org/EN/ProfessionalInterest/Pages/StatuteInternationalCriminalTribunalForRwanda.aspx>. 668 United States Supreme Court, Ex Parte Milligan, 1866, <http://www.law.cornell.edu/supremecourt/text/71/2>. 669 United States Supreme Court, Ex Parte Quirin, 31 July 1942, <https://www.law.cornell.edu/supremecourt/text/317/1#writingUSSC_CR_0317_0001_ZO>. 670 In addition to law of war violations and other offenses, the MCA 2009 also specifies that military commissions may also try cases for violations of 10 U.S.C. §§ 904, 906, which relate to spying and aiding the enemy. MCA 2009, §§ 948b(a), 948d. See, also, MCA 2006, § 948b(a). 671 For instance, the MCA 2009 defines and lists 32 offences. The listed offences are: murder of protected persons, conspiracy, attacking civilians, attacking civilian objects, attacking protected property, pillaging, denying quarter, taking hostages, employing poison or similar weapons, using protected persons as a shield, torture, cruel or inhuman treatment, intentionally causing serious 130