Who are ISIS' American recruits?

Story highlights

  • Texas shooting suspect appeared to have pledged support for ISIS
  • Peter Bergen: Several dozen Americans have backed ISIS, most of them young and active on social media

Peter Bergen is CNN's national security analyst, a vice president at New America Foundation and a professor of practice at Arizona State University. He is the author of "Manhunt: The Ten-Year Search for bin Laden -- From 9/11 to Abbottabad." David Sterman is a program associate at New America.

(CNN)Elton Simpson -- one of the gunmen who opened fire Sunday at an event in Garland, Texas, that was celebrating cartoonists who had drawn pictures of the Prophet Mohammed -- appears to have declared his allegiance to ISIS in a tweet before the attack. Simpson also apparently had online ties to a British ISIS recruit believed to be in Syria.

Simpson, who was shot to death by police, is far from the only American who who has been drawn to the black flags of ISIS as well as to the al Qaeda affiliate in Syria known as the Nusra Front.