In law, the principle of aut dedere aut judicare (Latin for "either extradite or prosecute") refers to the legal obligation of states under public international law to prosecute persons who commit serious international crimes where no other state has requested extradition.
However, the Lockerbie case demonstrated that the requirement to extradite or prosecute is not a rule of customary international law.
The obligation arises regardless of the extraterritorial nature of the crime and regardless of the fact that the perpetrator and victim may be of alien nationality.
[1] It is generally included as part of international treaties dealing with an array of transnational crimes to facilitate bringing perpetrators to justice.
"[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.