>> over 100 americans have traveled to syria bastad to travel to syria. >> do we know who they are? >> we do know who they are. some have come back. we keep an eye on them. the fbi director talked about that. the issue is, those guys who come back pose a threat. .mall-scale attacks the homegrown extremist person never traveled. they sit in their basement on the computer reading this propaganda and decide i can blow something up. >> bostoniss guided marathon. >> a little bit of that. >> it wasn't a serious issue but it is that same mindset. limit thator us to threat altogether. it is too easy to become radicalized on the internet, pick up relatively unsophisticated explosive devices. >> what we think they are learning in syria? thehe concern is individuals going to syria. 15,000. of that number probably 2000 are from western countries. that is a big number. they go to syria. they become radicalized further. they become battle hardened in the conflict. a get trained on small arms and explosives. , theyally the westerners have western travel documents. it is easy to travel from the u.k