The Central Intelligence Agency thought for months that it had mistakenly shredded a massive U.S. Senate report on its use of waterboarding and other "enhanced interrogation techniques" before suddenly discovering that its copy had not been lost after all, an agency official said Tuesday.

"It's embarrassing and I have apologized," Christopher Sharpley, the acting CIA inspector general, told the Senate Intelligence Committee during his confirmation hearing as President Donald Trump's nominee for the position.

Championed by Democratic Sen. Dianne Feinstein when she chaired the Senate panel, the "torture report," as it is known, is the result of a six-year investigation into so-called enhanced interrogation techniques used by the CIA after the Sept. 11, 2001, terrorist attacks.