Règle correspondante
Mexico
Practice Relating to Rule 101. The Principle of Legality
Mexico’s Army and Air Force Manual (2009), in a section on the 1949 Geneva Convention III, states:
Judicial procedure must be regular, that is, it must include at least the following guarantees: the accused must be immediately informed of the particulars of the offence he is alleged to have committed, which must have constituted an offence at the time it was committed. 
Mexico, Manual de Derecho Internacional Humanitario para el Ejército y la Fuerza Área Mexicanos, Ministry of National Defence, June 2009, § 191.
In a section on the obligations of the occupying power under the 1949 Geneva Convention IV, the manual states:
B. In order to ensure that justice is observed, the courts can apply only those provisions of law which were applicable prior to the offence, and which are in accordance with general principles of law …
C. Judicial procedure must be regular, that is, it must include at least the following guarantees:
b. the crime with which the accused is charged must have constituted an offence at the time it was committed. 
Mexico, Manual de Derecho Internacional Humanitario para el Ejército y la Fuerza Área Mexicanos, Ministry of National Defence, June 2009, § 238(B) and (C)(b).