values that are in america. freedom is one of them. >> reporter: after 9/11 from the hiding place in yemen, the cleric became the leader of al-qaeda 2.0, the new generation of american recruits. dinal tall jihaddist the cleric fame mousily leverageed social networking to spread his ideology of hate. former c.i.a. veteran charlie allen was the first u.s. official to identify al-awlaki as threat to u.s. national security. >> it's good day for the united states. it takes away a propaganda. proselytizeer or recruiter. >> al-qaeda in yemen plots against the u.s. is considered the lethal network affiliate. what sets the group apart according to senior counterterrorism officials is bomb-maker who perfected an explosionive to evade traditional air security. the group leader a long-time aide to usama bin laden. >> there are hardened groups. probably number between 500 and 1,000 fighters out there.