The U.S. has a relatively new "Human Rights Violator and War Crimes Unit" responsible for investigation persons in the US who have been involved with genocide, torture, war crimes, murder and other serious human rights violations.
Anyone with information about a person who has committed such crimes and has entered or will attempt to enter the United States can call ICE with a tip. The phone number is 1-866-347-2423. Calls can be anonymous.
Victims can call 1-866-872-4973 for assistance.
More info at http://www.ice.gov/pi/news/factsheets/hrvc1.htm