Who besides the Justice Dept. has the legal standing to bring charges in a U.S. court against war criminals?

The War Crimes Act (1996) makes violation of various Hague, Geneva and Nuremburg protocols and treaties a United States federal offense. Who, then, can bring American war criminals to trial in a U.S. court? Please limit your answer to American courts! International tribunals cannot enforce U.S. law and do not have any jurisdiction over U.S. citizens, nor can they impose the death penalty, which is authorized by the War Crimes Act. While U.S. military personnel are subject to the UCMJ, a different federal law that also outlaws war crimes, that law does not apply to civilians. Note that the present Attorney General believes that the War Crimes Act does apply to officials of the U.S. government, but if the Justice Department will not proscecute them, who else can bring charges? If a federal grand jury can bring charges, how can ordinary citizens cause such a grand jury to be empaneled? I repeat, international tribunals are irrelevant to this question; do not bother mentioning them.