Islamic State's Acolytes and the Challenges They Pose to U.S. Law Enforcement [June 13, 2016] [open pdf - 809KB]
"Analysis of publicly available information on homegrown violent jihadist activity in the United States since September 11, 2001, suggests that the Islamic State (IS) and its acolytes may pose broad challenges to domestic law enforcement and homeland security efforts. […] Since 2014, the Islamic State (IS) has become the focal point for the bulk of homegrown violent jihadist terrorist plots. This includes instances in which people in the United States wanted to travel to Syria to fight with extremist groups in the nation's civil war as well as plots to strike domestic targets. Regarding the former, in early 2016, U.S. government officials estimated that about 250 Americans had traveled (or tried to travel) to Syria to fight in the civil war--about 25 had been killed. Regarding the latter, in recent congressional testimony, the Director of National Intelligence, James R. Clapper noted that homegrown actors 'will probably continue to pose the most significant Sunni terrorist threat to the U.S. homeland in 2016.'"
CRS Report for Congress, R44521
Federation of American Scientists: http://www.fas.org/sgp/crs/index.html