Responding to congressional subpoenas, the State Department security agents were asked how the Libyan terrorists stormed the mission and set parts of it on fire, how they were armed and how they killed four Americans, including Ambassador J. Christopher Stevens, sources with knowledge of the matter said. The agents also were asked about security breakdowns and whether the administration reacted appropriately to the Sept. 11, 2012, assault.

How those highly guarded and secret interviews came about was part of an increasingly bitter dispute between two branches of the federal government.

Prosecutors are under intense pressure to arrest and convict the terrorists, while the Republican-led House is determined to find who is responsible for any lapse in security that night, and whether the administration misled the public when officials initially said the attack stemmed from a protest.

Weeks before the interviews, top Justice Department officials repeatedly warned Rep. Darrell Issa (R-Vista) against doing so, saying it would seriously jeopardize any criminal prosecution of the terrorists. They wrote three times to the chairman of the House Committee on Oversight and Government Reform, strongly urging him not to insist on interviewing the agents.