Related Rule
Germany
Practice Relating to Rule 100. Fair Trial Guarantees
Section N. Non bis in idem
Germany’s Military Manual (1992) provides: “Prisoners of war may not be punished or disciplined more than once for the same act.” 
Germany, Humanitarian Law in Armed Conflicts – Manual, DSK VV207320067, edited by The Federal Ministry of Defence of the Federal Republic of Germany, VR II 3, August 1992, English translation of ZDv 15/2, Humanitäres Völkerrecht in bewaffneten KonfliktenHandbuch, August 1992, § 725.
In 2010, in the Italian Partisans case, Germany’s Federal Court of Justice was called upon to decide a case concerning the killing of nine Italian civilians in Tuscany in June 1944 by German troops. The accused, who was a German officer at the time, had been convicted of ten counts of murder by a German regional court. In his appeal, the accused claimed that his trial had violated the principle of ne bis in idem. The Court held:
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1. … [O]n 28 September 2006, a military court in La Spezia (Italy) already sentenced the accused in absentia to life imprisonment for his acts [in Tuscany in June 1944].
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a) The prohibition of double jeopardy under Article 54 of the [1990] Convention Implementing the Schengen Agreement … is not breached in this case. This provision is in principle applicable to judgments rendered after trials at which the accused was not present. The application of this provision [Article 54 of the Convention Implementing the Schengen Agreement] requires that the judgment of 28 September 2006 has either already been executed, is being executed at the moment or can no longer be executed under the law of the State which rendered the judgment (in this case: Italy). All this is not the case. The prison sentence rendered in Italy is not being executed. However, the sentence could be executed under Italian law, as the competent Italian authority confirmed …
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(1) Italy has not yet requested the extradition of the accused. There are not concrete reasons to consider that this might change. …
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(2) Neither has Italy requested Germany to execute the judgment of 29 September 2006. …
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All in all, it follows that the judgment of 28 September 2006 does not constitute a procedural bar because for both legal and practical reasons, the execution of the judgment is not to be expected in Italy or Germany. 
Germany, Federal Court of Justice, Italian Partisans case, Decision, 25 October 2010, §§ 6–7 and 10–12.
Upon ratification of the 1977 Additional Protocol I, Germany stated:
Article 74, paragraph 4, subparagraph (h) of Additional Protocol I will only be applied to the extent that it is in conformity with legal provisions which permit under special circumstances the re-opening of proceedings that had led to final conviction or acquittal. 
Germany, Declarations made upon ratification of the 1977 Additional Protocols I and II, 14 February 1991, § 8.