Previously classified letters between Osama bin Laden and a high-ranking Al Qaeda operative reveal that the Afghan government used a secret fund, bankrolled by the CIA, to facilitate the release of a senior Afghan official kidnapped by the terrorist organization in 2010, The New York Times reports.

According to the Times, at least $1 million of the $5 million ransom payment was money that had come from the CIA. The exchange is referenced in letters between Osama Bin Laden and his second-in-command, Atiyah Abd al-Rahman, killed by a drone strike in 2011.

The letters were obtained during the deadly 2011 raid on Bin Laden's Abbottabad, Pakistan compound; they were entered as evidence by federal prosecutors in the trial of Abid Naseer, a Pakistani Qaeda operative, convicted this month in Brooklyn.

The Times reports that throughout Afghan President Hamid Karzai's time in power, the CIA made monthly deliveries to the presidential palace, dropping off bags of money. "It's cash," a former Afghan security official told the Times. "Once it's at the palace, they can't do a thing about how it gets spent."

The amounts reportedly ranged from a few hundred thousand dollars to more than $1 million:

The money was used to buy the loyalty of warlords, legislators and other prominent—and potentially troublesome—Afghans, helping the palace finance a vast patronage network that secured Mr. Karzai's power base. It was also used to cover expenses that needed to be kept off the books, such as clandestine diplomatic trips, and for more mundane costs, including rent payments for the guesthouses where some senior officials lived.

The $5 million ransom payment was for the release of Abdul Khaliq Farahi, who had been serving as the Afghan consul general in Peshawar, Pakistan when he was kidnapped in September 2008, the Times reports. Farahi—son-in-law to a man who had been a mentor to Karzai—was held for more than two years.

When the payment came through, Rahman complained to Bin Laden that other militant groups wanted to get in on the action. "As you know, you cannot control the news," Rahman wrote. "They are asking us to give them money, may God help us."

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