Tucked at the end of a Sept. 10, 1998, intelligence report sent to President Bill Clinton’s White House was a warning about Al Qaeda: the group “may fly an explosive-packed airplane into a U.S. city.” On Friday, the 25th anniversary of the Sept. 11 attacks, the C.I.A. released 69 never-before-seen presidential intelligence briefs detailing what it had discovered about Osama bin Laden and Al Qaeda in the run-up to the day.

The release is the agency’s largest focused on the attacks. The documents do not contain major new revelations and remain redacted. They reinforce the findings of the 2004 National Commission report: U.S. intelligence warned about Al Qaeda consistently but failed to understand the scale of the attack. C.I.A. Director John Ratcliffe said the documents honor the memory of those killed and the officers who gave their lives.

The briefings show the C.I.A. repeatedly brought the threat posed by bin Laden to Presidents Clinton and George W. Bush. Analysts said terrorist threats were not a primary focus before Sept. 11, and collection was spotty. A small group worked on terrorism, but it was nothing like the priority it became on Sept. 12, 2001.