We will not know for sure how much garbage or non-garbage the CIA gleaned from torturing captives until a Truth Commission sorts it all out, but we do have a great deal of evidence that torturing KSM was, pace Thiessen, not responsible for foiling the LA Tower plot. As Tim Noah notes, there is a matter of chronology:
In a White House press briefing, Bush's counterterrorism chief, Frances Fragos Townsend, told reporters that the cell leader was arrested in February 2002, and "at that point, the other members of the cell" (later arrested) "believed that the West Coast plot has been canceled, was not going forward" [italics mine]. A subsequent fact sheet released by the Bush White House states, "In 2002, we broke up [italics mine] a plot by KSM to hijack an airplane and fly it into the tallest building on the West Coast." These two statements make clear that however far the plot to attack the Library Tower ever gotan unnamed senior FBI official would later tell the Los Angeles Times that Bush's characterization of it as a "disrupted plot" was "ludicrous"that plot was foiled in 2002. But Sheikh Mohammed wasn't captured until March 2003.