Related Rule
Germany
Practice Relating to Rule 65. Perfidy
Section B. Killing, injuring or capturing an adversary by resort to perfidy
Germany’s Law Introducing the International Crimes Code (2002) punishes anyone who, in connection with an international or non-international armed conflict, “treacherously kills or wounds a member of the hostile armed forces or a combatant of the adverse party”. 
Germany, Law Introducing the International Crimes Code, 2002, Article 1, § 11(1)(7).
In 2010, in the Chechen Refugee case, Germany’s Federal Administrative Court was called upon to decide whether a Russian refugee claimant from Chechnya had to be excluded from refugee protection because there were serious reasons for considering that he had committed a war crime in Chechnya in 2002 by killing two Russian soldiers and taking a Russian officer hostage. The Court held:
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bb) The perfidious killing of the two Russian soldiers under Art. 9 para. 2 sub-para. e no. IX of the [1998] ICC Statute must be examined more closely.
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In order to define more concretely the requirements of “treacherous killing”, one can draw from the prohibition of perfidy in international armed conflict under Art. 37 para. 1 of the Additional Protocol I to the Geneva Conventions of 12 August 1949 relative to the Protection of Victims of International Armed Conflicts of 8 June 1977 … , which is also pertinent in non-international armed conflict.
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However, concerning non-international armed conflict it must be taken into account that there is no obligation of guerrilla or resistance fighters to wear uniform. Thus, the crime of feigning the status of a civilian or non-combatant is only fulfilled under special conditions. However, resistance fighters in non-international armed conflict are obliged to carry their weapons openly in order to facilitate the distinction between fighters and civilians. This follows from the provision of Art. 44 para. 3 [of the 1977] Additional Protocol I according to which combatants do not violate the prohibition of perfidy if they carry their weapons openly during each military operation including the preparation of attacks. This assessment must also be considered in the application of the prohibition of perfidy in non-international armed conflict …
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… Assuming that the appellant was directly participating in hostilities (on this matter see Art. 13 para. 3 Additional Protocol II …), it is possible that the appellant acted perfidiously because he did not indicate his direct participation in hostilities by carrying weapons openly or in any other way. In this case, he would have concealed that at the pertinent moment in time he was not entitled to protection and could have been attacked (see the interpretative guidance of the International Committee of the Red Cross on the notion of direct participation in hostilities …) By hiding their weapons, the attackers mislead the Russian soldiers into believing that they did not have to anticipate an attack from the resistant fighter and the appellant and that they were therefore not allowed to attack them. 
Germany, Federal Administrative Court, Chechen Refugee case, Judgment, 16 February 2010, §§ 36, 38 and 40–41.