Extremist Population News Today

Planned the 9/11 attacks, and they have reason to be, concerned. >> reporter: at least 100 americans flooded into syria since the start of the civil war, and u.s. ish tos fear many more may already be joining a bloody belgts, getting expert training how to plot attacks once back in the u.s. >> syria remains a significant destination for our home-grown violent extremist population. >> reporter: even more frightening, sources say, its a group becoming increasingly difficult to track. >> there isnt...