Frederick Hill was subpoenaed by Oversight Committee to appear . The panel says new information on the attack prompted its request for testimony . The terror attack in Oversight Committee killed three Americans . The attack on the U.S. diplomatic compound in eastern Libya killed Ambassador Christopher Stevens and three other Americans . NEW : Oversight Committee hearing set for September 2012 .
Frederick Hill was subpoenaed by Oversight Committee to appear . The panel says new information on the attack prompted its request for testimony . The terror attack in Oversight Committee killed three Americans . NEW : Oversight Committee hearing set for September 2012 .