The 9/11 commission's report does not fix blame for how the worst terror attack in US history was able to take place. But the nearly 600 pages of conclusions - after more than 1,300 interviews and the review of 2 million documents - are full of shoulda-woulda-couldas detailing moments when the attacks might have been thrown off or reduced in scale, if not fully prevented.
The details range from events where better follow-through could have made a difference - such as a crucial meeting of Al Qaeda operatives in Kuala Lumpur in January 2000 - to disregarded FBI field reports and even lax security checks of the hijackers on Sept. 11. In all, they're both heartbreaking and instructive.
While the "could this have been prevented?" debate may never be concluded, the commission's findings on what went wrong in specific instances are thus signposts for the future - even in instances where the conclusion is that a different response would not have guaranteed a foiling of the attacks.
For example, Al Qaeda's Kuala Lumpur meeting, already given substantial attention in part because of the presence of two hijackers - Nawaf al-Hazmi and Khalid al-Mihdar - gets fresh emphasis as a lost opportunity. The CIA loses track of them and they are never watch-listed, even though the CIA knows Mr. Hazmi holds a US visa. Still, the panel concludes that "even if watchlisting had prevented or alerted US officials to the entry of Hazmi and Mihdar, we do not think it is likely that would by itself have prevented the 9/11 attacks."
In its executive summary, the commission points to nine "operational opportunities" that it says constituted "points of vulnerability in the plot and opportunities to disrupt it."
In addition to the failure to watch-list Hazmi and Mr. Mihdar, they include not detecting false passports, not expanding no-fly lists to include names from terrorist watch lists, and not searching airline passengers identified on existing screening systems.
More broadly, the commission's report - the third major report on terrorism against the US in four years - raises the question of whether this time a report will be heeded more seriously. The other reports were released before Sept. 11. The conclusion among terrorism experts and policymakers is that the shock of that day means the new report will carry more weight.
Rep. Jane Harman (D) of California served on the National Commission on Terrorism in 2000 - whose final report concluded notably that Americans should expect a major terrorist attack soon on US soil. She recalls her frustration as late as Sept. 10, 2001, that the terror threat was not being paid more attention.