Story highlights CIA contractors who responded to terror attack in Libya will tell their story to Congress

Lawmakers have been pressing for witness accounts from the September 2012 attack

Ambassador Christopher Stevens and three other Americans were killed in attack

Benghazi has become a political flashpoint between Republicans and Obama administration

A House Intelligence subcommittee will hear from CIA security officers who are expected to tell a much more detailed story about the terror attack in Benghazi, Libya, that killed Ambassador Christopher Stevens and three other Americans last year, CNN has learned.

The men, described by sources as former Navy SEALs, former Army Special Forces and former Marines, were under contract to guard CIA agents on the ground there.

The security officers were among those who responded when Stevens' compound was attacked on the night of September 11, 2012.

They will appear before lawmakers behind closed doors during the week of November 11, sources told CNN.

Members of Congress have been trying to get access to the security officers and CIA agents, but those attempts have failed to date.

Photos: Photos: Attack on U.S. mission in Benghazi Photos: Photos: Attack on U.S. mission in Benghazi Attack on U.S. mission in Benghazi – Attackers set the U.S. mission in Benghazi, Libya, on fire on September 11, 2012. The U.S. ambassador to Libya, Christopher Stevens, and three other U.S. nationals were killed during the attack. The Obama administration initially thought the attack was carried out by an angry mob responding to a video, made in the United States, that mocked Islam and the Prophet Mohammed. But the storming of the mission was later determined to have been a terrorist attack. Hide Caption 1 of 22 Photos: Photos: Attack on U.S. mission in Benghazi Attack on U.S. mission in Benghazi – Obama and Clinton stand at Andrews Air Force Base as the bodies of the four Americans killed are returned on September 14. Hide Caption 2 of 22 Photos: Photos: Attack on U.S. mission in Benghazi Attack on U.S. mission in Benghazi – A desk sits inside the burnt U.S. mission on September 13, two days after the attack. Hide Caption 3 of 22 Photos: Photos: Attack on U.S. mission in Benghazi Attack on U.S. mission in Benghazi – Damage is seen inside the U.S. mission on September 13. Hide Caption 4 of 22 Photos: Photos: Attack on U.S. mission in Benghazi Attack on U.S. mission in Benghazi – A lounge chair and umbrella float in the swimming pool of the U.S. mission on September 13. Hide Caption 5 of 22 Photos: Photos: Attack on U.S. mission in Benghazi Attack on U.S. mission in Benghazi – Demonstrators gather in Libya on September 12 to condemn the killers and voice support for the victims. Hide Caption 6 of 22 Photos: Photos: Attack on U.S. mission in Benghazi Attack on U.S. mission in Benghazi – U.S. President Barack Obama, with Secretary of State Hillary Clinton on September 12, makes a statement at the White House about Stevens' death. Hide Caption 7 of 22 Photos: Photos: Attack on U.S. mission in Benghazi Attack on U.S. mission in Benghazi – A burnt vehicle is seen at the U.S. mission in Benghazi on September 12. Hide Caption 8 of 22 Photos: Photos: Attack on U.S. mission in Benghazi Attack on U.S. mission in Benghazi – People inspect the damage on September 12. Hide Caption 9 of 22 Photos: Photos: Attack on U.S. mission in Benghazi Attack on U.S. mission in Benghazi – A small American flag is seen in the rubble on September 12. Hide Caption 10 of 22 Photos: Photos: Attack on U.S. mission in Benghazi Attack on U.S. mission in Benghazi – A man stands in part of a burned-out building of the U.S. mission on September 12. Hide Caption 11 of 22 Photos: Photos: Attack on U.S. mission in Benghazi Attack on U.S. mission in Benghazi – Smoke and fire damage is evident inside a building on September 12. Hide Caption 12 of 22 Photos: Photos: Attack on U.S. mission in Benghazi Attack on U.S. mission in Benghazi – Half-burnt debris and ash cover the floor of one of the U.S. mission buildings on September 12. Hide Caption 13 of 22 Photos: Photos: Attack on U.S. mission in Benghazi Attack on U.S. mission in Benghazi – The U.S. mission is seen in flames on September 11, the day of the attack. Hide Caption 14 of 22 Photos: Photos: Attack on U.S. mission in Benghazi Attack on U.S. mission in Benghazi – A protester reacts as the U.S. mission burns on September 11. Hide Caption 15 of 22 Photos: Photos: Attack on U.S. mission in Benghazi Attack on U.S. mission in Benghazi – A vehicle and the surrounding area are engulfed in flames on September 11. Hide Caption 16 of 22 Photos: Photos: Attack on U.S. mission in Benghazi Attack on U.S. mission in Benghazi – Flames erupt outside of a building on September 11. Hide Caption 17 of 22 Photos: Photos: Attack on U.S. mission in Benghazi Attack on U.S. mission in Benghazi – A vehicle burns during the attack on the U.S. mission on September 11. Hide Caption 18 of 22 Photos: Photos: Attack on U.S. mission in Benghazi Attack on U.S. mission in Benghazi – Onlookers record the damage from the attack on September 11. Hide Caption 19 of 22 Photos: Photos: Attack on U.S. mission in Benghazi Attack on U.S. mission in Benghazi – Onlookers walk past a burning truck and building on September 11. Hide Caption 20 of 22 Photos: Photos: Attack on U.S. mission in Benghazi Attack on U.S. mission in Benghazi – A vehicle sits smoldering in flames on September 11. Hide Caption 21 of 22 Photos: Photos: Attack on U.S. mission in Benghazi Attack on U.S. mission in Benghazi – People duck flames outside a building on September 11. Hide Caption 22 of 22

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Of the estimated nearly two dozen CIA operatives on the ground that night, only one has testified, the sources said.

Frustrated lawmakers have told CNN they have been dissatisfied with the investigation so far conducted by House Intelligence Committee Chairman Mike Rogers, R-Michigan.

His staff defends the work of the committee, telling CNN previously the review has included nine full committee hearings, roundtable discussions with some Obama administration officials, an interim report and a vow that the investigation continues.

The members of Congress say they don't want information that's filtered like what they've gotten in briefings and documents, but that they want to hear the answers to three basic questions straight from those who were there:

One: What was the CIA doing in Libya? There have been allegations the CIA was operating a gun-running program with weapons going from Libya to Syrian rebels.

Two: What happened during the failed rescue attempts? CNN has been told that there was a group of would-be rescuers at the CIA annex, armed and ready to go within minutes of the attack, but they were held off until finally they defied orders and staged a rescue on their own.

Three: Did the administration know immediately that this was a planned terrorist attack? And if so, why did administration officials try to first claim it was a spontaneous response to a demonstration over a movie that offended Muslims?

"I think that there's a real mystery here surrounding what really took place and for reasons unbeknownst to me, the Congress as well as the agency are going out of their way to protect whatever there was that they were doing operationally in Libya," said Fred Burton, a former State Department diplomatic security agent who has written a book about Benghazi that's now being turned into an HBO movie.

And sources say the CIA has been trying to keep its employees quiet.

CNN reported previously that some operatives involved in the agency's missions in Libya have been subjected to frequent -- even monthly -- polygraph examinations to find out whether they've have spoken to Congress or the media, according to sources with deep inside knowledge of the agency's workings.

The CIA said in a statement this is "patently false."

"Not a single CIA officer who was on the ground in Benghazi during the attacks has been subjected to any CIA polygraph intended to discourage them from speaking to Congress or as retaliation," the agency told CNN.

"To date, some of these officers have already spoken to the oversight committees on Benghazi," it added.