The number of Muslim Americans associated with extremist plots peaked in 2015, according to a new report issued by the Triangle Center on Terrorism and Homeland Security. Eighty-one such individuals were identified last year, while the total number of Muslim Americans believed to be involved in extremist plots since the Sept. 11, 2001, terror attacks is 344, researcher Charles Kurzman reports. Kurzman adds that government officials continue to estimate that only about 250 Americans have joined ISIS in Syria—a number that has not changed since mid-2015. Some of them have been charged in the U.S., while others are presumed dead by authorities. Only one is believed to have gone to Syria with the intention of returning to carry out an attack on American soil.