Hassan was reportedly in Twitter contact with Elton Simpson, one of two gunmen killed by police after he opened fire at an event featuring cartoons of the Prophet Mohammed in Garland, Texas, in May, according to the Counter Extremism Project, a U.S. group formed to combat extremist ideology. He exhorted followers to build an Islamic caliphate -- the goal of Islamic State -- and to leave their home countries to be jihadists, according to the Anti-Defamation League.