ISIS Americans: Two suspected American ISIS fighters have been captured on a battlefield in Syria, Kurdish militants allied with the U.S. said this week. The Syrian Democratic Forces identified one of the Americans as Warren Christopher Clark, a 34-year-old former substitute school teacher from Houston. A convert to radical Islam, Clark was known as being so overtly pro-terrorism that acquaintances in Texas assumed he was an FBI informant. Using the name Abu Mohammad al-Ameriki, he allegedly sent a letter to ISIS asking for a job as an English teacher at the University of Mosul in Iraq. The other purported American was named as Zaid Abed al-Hamid; little is known about him, and some reports say he is actually from Trinidad. An estimated 64 Americans have traveled to Iraq and Syria to join ISIS since 2011.