In October 2013, the European Court of Human Rights ruled on claims brought against the Russian Federation for the 1940 massacre of more than 21,000 prisoners of war. Relatives of the prisoners challenged that Russia had, among other things, failed in its legal obligation to carry out an adequate and effective investigation into the massacre. The court concluded that it did not have temporal jurisdiction to evaluate the merits of these claims; it stated that Russia’s legal obligation to investigate could not extend to transgressions that occurred prior to the existence of the convention under which the claims had been brought. Unfortunately, in looking to the convention and not to international customary law as the source of temporal jurisdiction, the court was unable to protect the rights of the prisoners and their relatives. The court should have looked to customary law to establish temporal jurisdiction so that it could reach the merits of the case and hold Russia accountable for its gross violation of human rights.