ECCHR submitted in February 2010 an expert opinion on concurrent criminal jurisdictions under international law in a Spanish case. The opinion was written by ECCHR and its advisory board member Professor Dr. Florian Jeßberger. Spanish courts argued they were not competent to open investigations into international crimes committed in Gaza, because investigations were already opened by local authorities. The Gaza (Al Daraj) case concerns the targeted bombing of a house located within a built up area carried out by the Israeli air force in 2002. The attacks aimed to kill an alleged-leader of Hamas. 14 people were killed alongside the intended victim of the attacks. In addition around 150 people were injured and a significant amount of property was destroyed.

The ECCHR expert opinion concludes that states have a responsibility to open investigations into international crimes if there are no genuine investigations on-going in the territorial state in which the crime was committed. States are not limited by the fact that one state has already exercised its criminal jurisdiction over a crime by opening investigations. The expert opinion shows that there is no hierarchy of criminal jurisdictions in international law. A state exercising its criminal jurisdiction on the principle of personality or universality does not necessarily have to give priority to the state exercising territorial jurisdiction. Although there is a clear preference and policy favoring investigations by the territorial state, these investigations must meet universal standards e.g. as established by regional human rights courts. Inadequate investigations are a serious problem in many violations of international law. The consequences are a climate of impunity and the aggravation - or in the worst case - avoidance of later prosecution. Therefore, a state has the responsibility to open investigations if such investigations in another country do not meet universal standards.