Ruslan Maratovich Asainov, a naturalized U.S. citizen from Kazakhstan who lived in Brooklyn, left the United States in December 2013 to join the Islamic State in Syria, where he became a sniper, according to the Justice Department. Asainov allegedly became a high-ranking ISIS official who was tasked with training other ISIS members to use weapons. Syrian Democratic Forces captured Asainov in Syria, and he was turned over to U.S. authorities.