Congressional Research Service. February 15, 2012.
Criminal law is usually territorial. It is a matter of the law of the place where it occurs. Nevertheless, a number of American criminal laws apply outside of the United States. Application is generally a question of legislative intent, expressed or implied. In either case, it most often involves crimes committed aboard a ship or airplane, crimes condemned by international treaty, crimes relating to government employees or property overseas, or crimes that have an impact in this country even if planned or committed in part elsewhere.
http://www.fas.org/sgp/crs/misc/94-166.pdf [PDF format, 76 pages].