Year after Benghazi attack, investigators still lack info on specifics 11 (UPI) -- Several militant groups took part in the deadly 2012 attack on the U.S. Consulate in Benghazi, Libya, U.S. counter-terrorism officials determined. The officials identified numerous people involved - such as the extremist group Ansar al-Sharia -- and have issued sealed indictments in recent months, but on the one-year anniversary there isn't "anyone in custody who can tell us" specifics of the attack, a counter-terrorism official told The Washington Post in an interview published Tuesday. "That is a huge gap," said the official. What we lack is a source of information that puts us where we need to be. The Benghazi attack -- in which Christopher Stevens, the U.S. ambassador to Libya, and three other diplomatic employees died -- still is a live issue for investigators and House Republicans conducting hearings on whether the Obama administration is covering up failures that occurred before, during and after the assault. Throughout the summer, House Oversight Committee Chairman Darrell Issa, R-Calif., has had increasingly testy exchanges with the State Department officials and the independent Accountability Review Board appointed to investigate the attack. Last month, he issued two subpoenas for documents and, backed by Speaker John Boehner, plans to hold additional hearings in the fall, the Post said. On Tuesday, Issa sent a letter to Secretary of State John Kerry to complain about the State Department's foot-dragging in facilitating testimony of two Diplomatic Security agents at the CIA facility in Benghazi during the attack. One of the agents was severely wounded and remained hospitalized this summer.