ABC News reports that Wednesday’s suicide attack was the result of the unprecedented infiltration of the Agency by jihadi opponents employing a double agent who had successfully gained the trust of CIA officers.

The losses inflicted by the suicide attack were key personnel central to the Agency’s drone attack program whose regional expertise and experience will be very difficult to replace.

The suicide bomber who killed at least six Central Intelligence Agency officers in a base along the Afghan-Pakistan border on Wednesday was a regular CIA informant who had visited the same base multiple times in the past, according to someone close to the base’s security director.

The informant was a Pakistani and a member of the Wazir tribe from the Pakistani tribal area North Waziristan, according to the same source. The base security director, an Afghan named Arghawan, would pick up the informant at the Ghulam Khan border crossing and drive him about two hours into Forward Operating Base Chapman, from where the CIA operates.

Because he was with Arghawan, the informant was not searched, the source says. Arghawan also died in the attack.

The story seems to corroborate a claim by the Taliban on the Pakistani side of the border that they had turned a CIA asset into a double agent and sent him to kill the officers in the base, located in the eastern Afghan province of Khost.

The infiltration into the heart of the CIA’s operation in eastern Afghanistan deals a strong blow to the agency’s ability to fight Taliban and al Qaeda, former intelligence officials say, and will make the agency reconsider how it recruits Pakistani and Afghan informants.

The officers who were killed in the attack were at the heart of the United States’ effort against senior members of al Qaeda and the Taliban, former intelligence officials say. They collected intelligence on the militant commanders living on both sides of the border and helped run paramilitary campaigns that tired to kill those commanders, including the drone program that has killed a dozen senior al Qaeda with missiles fired from unpiloted aircraft.

The former intelligence officials all say the CIA will be able to replace those who were killed, but the officials acknowledge the attack killed decades of knowledge held by some of the agency’s most informed experts on the region, the Taliban and al Qaeda. It also killed at least one officer who had been part of the agency’s initial hunt for Osama bin Laden in the mid-1990s.

“This is a tremendous loss for the agency,” says Michael Scheuer, a former CIA analyst who led the bin Laden unit. “The agency is a relatively small organization, and its expertise in al Qaeda is even a smaller subset of that overall group.”

At least 13 officers gathered in the base’s gym to talk with the informant, suggesting he was highly valued. His prior visits to the base and his ability to get so close to so many officers also suggests that he had already provided the agency with valuable intelligence that had proven successful, former intelligence officials say.

That information was most likely linked with the CIA’s drone program on the Pakistani side of the border. …

The most likely Taliban group to have perpetrated the attack is the one led by Sirajuddin Haqqani, the son of Jalaluddin Haqqani, one of the CIA’s most important assets when the agency was helping fund the Afghan mujahedeen fighting the Soviets in Afghanistan. The Haqqanis have been running militant operations for 30 years and have recently become perhaps the most lethal commanders targeting U.S. troops in Afghanistan. They are based in North Waziristan but control large parts of Khost and other provinces in eastern Afghanistan as well.

The Haqqanis have also kidnapped the only known American soldier in enemy custody — PFC Bowe Bergdahl — according to a senior NATO official. Since Bergdahl was kidnapped in late June, the official says the Haqqanis “have been getting pounded” and a “great many of their mid to senior leaders have been captured and/or killed.”

The infiltration into the CIA base suggests an extremely high level of sophistication, even for a network that has a huge reach across the area.

“The Soviet Union during the Cold War, the Cubans during the Cold War were able to run double agents against the CIA very successfully,” says Clarke. “But for a non-nation state to be able to do this — for the Haqqani network of the Taliban to be able to do this — represents a huge increase in the sophistication of the enemy.”

Clarke and other former intelligence officials predict the CIA in Afghanistan will be forced to question who they can trust and change their methods in how they find informants.

The only victim of the attack who has been publicly identified is 37-year-old Harold Brown Jr., a father of three. The base chief, a woman in her 30s, was also killed, according to current and former intelligence officials. She is believed to have been focused on al Qaeda since before 9/11. A former U.S. official says a second woman was also killed in the attack, and that both women had “considerable counterintelligence experience.”

The attack also killed Captain Al Shareef Ali bin Zeid, a member of the Jordanian spy agency Dairat al-Mukhabarat al-Ammah, according to people who have spoken with bin Zeid’s family. The Jordanian military released a statement acknowledging bin Zeid had been killed in Afghanistan, but did not mention he was working with the CIA.

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