The name for the concern about infringement upon sovereignty by arresting a citizen, in this case, in another state is &quot;extraterritoriality&quot;.<p>There is a presumption against extraterritoriality.  In other words, it is presumed that in a sovereign state the laws of other sovereigns do not apply.<p>The exception to the presumption against extraterritoriality is agreement among states or a reciprocal judicial respect.  The agreement is usually a treaty. The reciprocal respect is called &quot;comity&quot;.<p>There are other exceptions to the presumption against extraterritoriality, but I do not think they apply here.<p>I have not looked at the details, but New Zealand and the U.S.A. must have an extradition treaty or otherwise the judge determining extradition believes that the judicial system in the U.S.A. is &quot;comparable&quot; (i.e. comity applies).<p>The case looks appealable.  So long as the independence of the judiciary is not impugned, neither is the sovereignty of New Zealand, and they may extradite as they feel fit.