Over the past year, the al-Qaeda leader fielded e-mails from followers lamenting the toll being taken by CIA drone “explosions” as well as the network’s financial plight, according to U.S. officials who have completed an exhaustive review of the trove of bin Laden files collected at his compound after the May 2 U.S. raid that killed him.

Bin Laden approved the creation of a counterintelligence unit to root out traitors and spies, only to receive a complaint in mid-2010 from the unit’s leader that it was losing the “espionage war” and couldn’t function on its paltry budget…

One of bin Laden’s principal correspondents was Atiyah abd al-Rahman, who served as No. 3 in al-Qaeda before bin Laden’s death. A 2010 message from Rahman expressed frustration with the CIA drone campaign, a source of particular concern because many of his predecessors in the third-ranking slot had been killed in strikes by the unmanned aircraft.

“He was saying in the letter that their guys were getting killed faster than they could be replaced,” the U.S. counterterrorism official said.