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."[2] But in the international crimes for which it is applied, it is "posited [by Cherif Bassiouni] that ... it is not only a rule of customary international law but a jus cogens principle", compelling states to invoke it for any and all crimes that fall under the principle; Kelly finds within Israeli and Austrian judicial decisions "some supporting anecdotal evidence that judges within national systems are beginning to apply the doctrine on their own."[3]