jihadists overseas. they're now trying to determine if he was trying to get the jihadists' attention or plotting with them. the use of social media by terrorists is a daunting challenge. >> it allows like never before for overseas groups to reach into oir communities to recruit, to radicalize as well as to target our citizens. all in a very simple easy-to-use way. >> reporter: back on april 10th in a private twitter message intercepted by the u.s. cnn is told that simpson discussed with others how to get to syria. bring your passport. if you have $4,000 that's enough to travel he wrote. and hours before the attack simpson urged his twitter followers to follow a known british intelligence hacker a significant figure in isis. >> somebody known as a propagandist within isis somebody known for his hacking skills who has targeted the u.s. military in previous hacks. >> reporter: tonight, we are learning more about the gunmen's