Bergen 2006 Scheuer 2002 Leaderless Jihad: Terror Networks in the Twenty-First Century Marc Sageman University of Pennsylvania Press January 3, 2008.
2011년 2월 11일에 확인함.  Bergen 2006 Scheuer 2002 Leaderless Jihad: Terror Networks in the Twenty-First Century Marc Sageman University of Pennsylvania Press 2008년 1월 3일.