Former Hillary Clinton aide, during her tenure as Secretary of State, Jake Sullivan, right, arrives to be interviewed before a House panel on the Benghazi investigation on Capitol Hill in Washington, Friday, Sept. 4, 2015. Sullivan, a former policy director and deputy chief of staff at the State Department, will be questioned Friday in what is expected to be a daylong session. (AP Photo/Cliff Owen)

WASHINGTON | The chairman of a congressional panel investigating the deadly Benghazi attacks says a member of Hillary Rodham Clinton’s inner circle could provide key insight into how the State Department maintained its presence in Libya prior to the 2012 attack.

Former Hillary Clinton aide, during her tenure as Secretary of State, Jake Sullivan, right, arrives to be interviewed before a House panel on the Benghazi investigation on Capitol Hill in Washington, Friday, Sept. 4, 2015. Sullivan, a former policy director and deputy chief of staff at the State Department, will be questioned Friday in what is expected to be a daylong session. (AP Photo/Cliff Owen)

Jake Sullivan, a former policy director and deputy chief of staff at the State Department, arrived early Friday for what is expected to be a daylong session.

Republican Rep. Trey Gowdy of South Carolina says Sullivan was in a “unique position” to talk about how U.S. policy in Libya required the State Department to have a physical presence in the country.

The attack on the U.S. diplomatic facilities in Benghazi killed four Americans, including the U.S. ambassador to Libya.

The panel interviewed former Clinton chief of staff Cheryl Mills for 9½ hours on Thursday.