The intelligence community did not complete a comprehensive analysis of al-Qaida until 1999, almost a full decade after bin Laden started the terrorist organization, according to the staff report. As late as 1997, the agency's Counterterrorism Center described bin Laden as a "financier of terrorism," despite intelligence that showed bin Laden headed an organization that included operational commanders and an agenda for targets, the report found.

And the description of bin Laden as a terrorist financier belied the evidence that bin Laden had planned terrorist attacks that included a Yemen hotel where U.S. military personnel were stationed in 1992; shooting down Army Blackhawk helicopters in Somalia in 1993; and possibly the 1995 Riyadh bombing of the American training mission to the Saudi Arabian National Guard. Nor had analysts answered questions about links between al-Qaida and the bombing of the World Trade Center in 1993, the report states.

Despite the information flowing into the agency, a comprehensive intelligence report, known as a National Intelligence Estimate, failed to mention the terrorist group's intentions to attack the United States.

The agency produced analytical papers about bin Laden's political philosophy, his global network and his operational style, investigators for the 9-11 Commission said, but "there were no complete authoritative portraits of his strategy and the extent of his organization's involvement in past terrorist attacks."

"Most important, our interviews of senior policymakers in both administrations revealed a fundamental uncertainty about how to regard the threat posed by bin Laden and al-Qaida," the report states.

For example, when a CIA analyst developed a comprehensive paper on bin Laden in 1998, her supervisor "did not consider the paper publishable" in an internal report given to top intelligence officials. He broke the topic down into four separate papers assigned to four other analysts and it took more than two years for two of the four papers to be published. The remaining two papers were not completed until after the Sept. 11 attacks, according to the staff report.

Former CIA officials, including a past chief of the Counter Terrorism Center, downplayed the threat from al-Qaida before the attacks. One even attributed it to "overheated rhetoric," according to the report.

"Before the attack, we found uncertainty among senior officials about whether this was just a new and especially venomous version of the ordinary terrorist threat America has lived with for decades, or was radically new, posing a threat beyond any yet experienced."

Tenet took issue with the staff report's conclusion that it didn't take al-Qaida seriously enough.

"That's flat wrong," Tenet said.