 It is, however, unusual for states to be required to exercise this jurisdiction because often another state party will have an interest in the matter, and so will apply for extradition of the defendant(s).In this situation the state requesting extradition will have priority.The obligation of "aut dedere aut judicare" for all crimes is however not assured, and Stigall notes that "some contemporary scholars hold the opinion that "aut dedere aut judicare" is not an obligation under customary international law but rather “a specific conventional clause relating to specific crimes” and, accordingly, an obligation that only exists when a state has voluntarily assumed the obligation."