Major findings by the Sept. 11 commission in its final report:

— Unsuccessful diplomacy. From 1997 to Sept. 11, 2001, the U.S. government unsuccessfully tried diplomatic pressure to persuade the Taliban regime in Afghanistan to stop providing sanctuary to Al Qaeda (search). U.S. officials couldn't persuade the United Arab Emirates, one of the Taliban's only financial outlets to the outside world, to cut off Taliban ties. The Saudi and U.S. governments did not fully share intelligence information or collaborate to disrupt Al Qaeda finances.

— Lack of military options. Senior military officials and policy-makers placed great emphasis on "actionable intelligence" in deciding whether to strike Usama bin Laden (search). On three occasions in 1998-1999, intelligence was credible enough to warrant planning for possible strikes, but policy-makers decided the risks of error outweighed the benefits.

— Intelligence failures. Agencies struggled during the 1990s to collect intelligence on the developing terrorist threat, but were hobbled by flat budgets, an outdated structure and bureaucratic rivalries. While there were many reports on bin Laden, no comprehensive review was undertaken to analyze them. The CIA was constrained by using proxies to try and capture bin Laden and his associates in Afghanistan.

— FBI troubles. FBI and Justice officials became increasingly concerned during the 1990s about a terror threat from Islamic extremists to the United States. But significant resources were devoted to case-specific prosecutions and after-the-fact investigations of terror attacks rather than prevention.

— Weak border and immigration controls. The 19 hijackers included known Al Qaeda operatives who could have been put on government watch lists; presented fraudulent or otherwise suspicious-looking passports; made false statements to border officials; and violated immigration laws. Yet none were caught, in part because border protection was not a national security issue before Sept. 11, 2001.

— Weak aviation security. Hijackers studied publicly available information on aviation security to exploit weaknesses. They slipped through airport security checkpoints even after being selected for extra baggage screening. While two of the hijackers were on a government terrorist watch list, the Federal Aviation Administration did not use the data.

— Terrorist financing. The hijacking plot cost somewhere between $400,000 and $500,000 to execute. The conspiracy made extensive use of U.S. banks, with hijackers opening accounts in their own names and using passports, but their transactions were unremarkable and essentially invisible. It is still unknown where the money came from, but Al Qaeda had many sources of funding; if one dried up, others were available.

— Vulnerable homeland security. Confusion reigned among FAA (search) and military officials the day of the attacks. FAA officials trained to respond to a traditional hijacking, not a suicide attack, were slow to alert the military, and some military fighter pilots were never told why they were scrambled. Communication was poor.

— Slow emergency response. Basic flaws in New York City's emergency 911 phone system denied people inside the World Trade Center potentially lifesaving information. With the buildings' public address systems out of service, workers inside who called 911 for help were told not to evacuate. Communication was poor among first responders, due in part to a lack of operating procedures and substandard radios.

— Poor congressional oversight. Congress was slow to recognize the growing terror threat; it also gave little guidance to executive branch agencies. It did not perform robust oversight to identify and resolve apparent problems in national security and domestic agencies that were readily apparent after Sept. 11.