Norma relacionada
Peru
Practice Relating to Rule 101. The Principle of Legality
Peru’s IHL Manual (2004) states that a person charged with a criminal offence under international humanitarian law must be provided with certain guarantees, including: “application of the law in force at the time the offence was committed; the effect of criminal law provisions cannot be retroactive”. 
Peru, Manual de Derecho Internacional Humanitario para las Fuerzas Armadas, Resolución Ministerial Nº 1394-2004-DE/CCFFAA/CDIH-FFAA, Lima, 1 December 2004, § 32.n.(3).
Peru’s IHL and Human Rights Manual (2010) states that a person charged with a criminal offence under international humanitarian law must be provided with certain guarantees, including: “[a]pplication of the law in force at the time the offence was committed; [the effect of criminal law provisions] cannot be retroactive.” 
Peru, Manual de Derecho Internacional Humanitario y Derechos Humanos para las Fuerzas Armadas, Resolución Ministerial No. 049-2010/DE/VPD, Lima, 21 May 2010, § 33(n)(3), p. 251.
Peru’s Code of Military and Police Justice (2006) states:
Nobody may be convicted without a trial based on law that predates the act for which the person is prosecuted. The trial must fully respect the rights and guarantees established in the Political Constitution [of Peru], in international treaties for the protection of human rights and the norms in the present Code. 
Peru, Code of Military and Police Justice, 2006, Article 150.
Peru’s Military and Police Criminal Code (2010), which includes provisions on crimes under international humanitarian law, states in the Preliminary Title:
No member of the military or the police may be investigated, judged or punished for an act or omission which was not expressly and unequivocally established as a crime committed in the line of duty by the criminal law in force at the time of its commission. 
Peru, Military and Police Criminal Code, 2010, Article IV.
In 2004, in the Gabriel Orlando Vera Navarrete case, Peru’s Constitutional Court stated:
The lex praevia guarantee derived from the principle of legality is not violated in the case of a continuing crime if a criminal law is applied that was not in force before the point in time when the execution of the crime began but which has entered into force while the crime was being committed. Thus, the fact that the crime of enforced disappearances was not in force does not impede a criminal prosecution for this crime and the punishment of those responsible. 
Peru, Constitutional Court, Gabriel Orlando Vera Navarrete case, Case No. 2798-04-HC/TC, Judgment, 9 December 2004, § 22.
In 2006, in the Colegio de Abogados de Lima case, Peru’s Constitutional Court stated:
22. As such, the principle of legality ensures: a) the prohibition against retroactive application of criminal law (lex praevia); b) the prohibition of analogy (lex stricta); c) the prohibition of indeterminate legal provisions (lex certa); and d) the prohibition against the application of non-statutory law (lex scripta).
23. In conformity with its lex praevia component, the principle of legality prohibits the retroactive application of criminal law, except of course when its application benefits the accused.
25. … [T]he principle of legality requires not only that the crimes be defined by law, but also that the prohibited conduct be clearly delimited in the law. This is known as the certainty requirement, which prohibits the enactment of indeterminate criminal laws.
26. With regards to the lex scripta requirement, the principle of legality establishes that the accusation and punishment of criminal behaviour be based solely on statutory law, prohibiting, among other issues, basing punishment on customary law. 
Peru, Constitutional Court, Colegio de Abogados de Lima case, Case No. 0012-2006-HC/TC, Judgment, 15 December 2006, §§ 22–23 and 25–26.
In 2007, in the Chuschi case, the Permanent Criminal Chamber of Peru’s Supreme Court of Justice stated:
[I]n order to avoid breaching the constitutional rule of non-retroactive application of the law, the continuous act [of enforced disappearance] shall be punished under the law that defined the crime if the perpetrator commits the acts fully or partially after the law’s entry into force. The unlawful situation generated by the perpetrator, which encompasses the entire period until the consummation of the offence, must reach the new law’s date of entry into force. 
Peru, Supreme Court of Justice, Permanent Criminal Chamber, Chuschi case, Case No. 1598-2007, Judgment, 24 September 2007, pp. 161–162.
In 2007, in the Castillo Páez case, the First Provisional Criminal Chamber of Peru’s Supreme Court of Justice stated with regard to the offence of enforced disappearance:
[T]he events of this case occurred on 21 October 1990 (before the current Criminal Code, which contains the crime of enforced disappearance, entered into force). But since enforced disappearance is a continuous crime, it shall be interpreted to have been committed under the current Code and the provisions of this Code shall be considered applicable. Although in constitutional criminal matters the general rule of “lex praevia” applies (by which the norm must exist prior to the commission of the criminal act), the situation described above constitutes the continuous commission of an unlawful act, prolonged in time, and defined by the new law (given that the whereabouts of the victim continue to be unknown). In this sense, it is worth noting that if the accused have committed the unlawful act constituting the crime which is continuous covered by the new law in force, there is no doubt that the law is applicable with no retroactive effect ad malam partem. This has been the position of the Constitutional Court in the following cases: docket no. 2488-2002-HC/TC, the Genaro Villegas Namuche case (judgment of 18 March 2004, para. 26); docket no. 2529-2003-HC/TC, Peter Cruz Chávez case (judgment of 2 July 2004, para. 3); docket no. 467-2005-PHC/TC Juan Nolberto Rivero Lazo case (judgment of 12 August 2005, para. 25); docket no. 0442-2007-HC/TC, Collins Collantes Guerra case (judgment of 30 March 2007, para. 6). 
Peru, Supreme Court of Justice, First Provisional Criminal Chamber, Castillo Páez case, Case No. 0012-2006-HC/TC, Judgment, 18 December 2007, § 3(v).