The doctrine of sovereign immunity is a long standing and well established doctrine. Without it, international relations would not be possible since members of govenments would be subject to arrest by host countries. Any lifting of sovereign immunity must be done with caution, for good cause, and with reciprocity. Under US law, war crimes against members of foreign governments can be prosecuted if that state is declared a terrorist state. In general, war crimes should be prosecuted by ad hoc international tribunals. The idea that individuals can appoint themselves to prosecute such crimes in domestic courts when the crime, the plaintiff and the supposed perpetrator are all in a third country, is bound to bring chaos into international relations. The politisation of war crime prosecutions does nothing but undermine confidence in the workings of international treaties, and generally into the workings of public international order.
Mexico sentences five men to 697 years for killings of 11 women (AP)
from the article: U.S. District Court in Manhattan clears Dichter in war crimes suit