With countless police, intelligence and journalistic examinations and two special congressional inquiries, the Sept. 11 attacks have been among the most investigated criminal acts in history.
The release last week of the final report of the independent 9/11 commission offered the nation a comprehensive overview of the origin and execution of the attacks. What the nation does not have are answers to all the outstanding questions, some of them fundamental:
Who provided the nearly half a million dollars it cost to carry out the attacks? How could the man who is alleged to have recruited several of the hijack pilots have done this while under investigation by at least three intelligence services -- those of the United States, Germany and Morocco? Who, if anyone, assisted the hijackers during their time in the United States?
Some unanswered questions fall more in the category of perplexing curiosities:
Why did Mohamed Atta and another hijacker drive from Boston to Portland, Me., the day before the attacks, then fly back to Boston the next morning, almost missing the flight they intended to hijack?
Still other questions have less to do with the plot itself than the ground from which it sprung:
How did it happen that a single family of Pakistani expatriates in Kuwait, by most accounts an ordinary, pious family devoted to good works, produce five men -- the plot mastermind, Khalid Shaikh Mohammed, and four of his nephews -- who played roles in the attacks?
Many of the open questions might never be resolved. As commission Chairman Thomas H. Kean acknowledged, "There are still some unanswered questions because obviously the people who were at the heart of the plot are dead."
The independent 9/11 commission, formally known as the National Commission on Terrorist Attacks Upon the United States, performed best on the issues it investigated firsthand, which largely were the U.S. government's actions and inactions. Most of its 1,200 interviews dealt with this subject. For information on the plot itself, the commission dealt primarily with reports of investigations by others.
That other reporting by necessity relied on sources of varying credibility. The account of the origin and details of the hijack plot itself come almost entirely from hostile interrogations of two men -- Mohammed and one of his deputies, Ramzi Binalshibh, both of whom are in U.S. custody, but neither of whom has shown much willingness to talk about matters that might implicate others.
Binalshibh, for example, has told his interrogators that two events in the plot were instigated by separate chance encounters on German trains. One of the events pertained to the decision of the Hamburg-based hijackers to travel to Afghanistan in 1999. Binalshibh said the decision was made after a chance meeting on a train with a man who told him to contact a third man who could tell him how to join the jihad. The man on the train approached him because he spoke Arabic and had a beard, Binalshibh said. Investigators, trained to distrust coincidence, wondered at the odds of that.
Also, according to footnotes in the commission report, much of the information on the personalities of the lead hijackers comes from a single German source, a Hamburg teenager who knew the hijackers but did not speak Arabic.
Here are some of the open questions and what, if anything, is known about their answers.
* Who provided the nearly half a million dollars the attacks cost?
The money was passed from Mohammed to the hijackers by electronic transfer and courier through the United Arab Emirates. Where Mohammed got the money is unknown. He said it came from Osama bin Laden's personal fortune, but investigators have found that the Al Qaeda leader's wealth has been vastly overestimated and that almost all of the organization's estimated $30-million-a-year budget was funded by donations.
Who made the donations to Al Qaeda is unknown. Mohammed first came to the attention of American investigators for his fundraising activities in the Persian Gulf, leading some to suspect he might have raised much of the relatively modest 9/11 sum on his own.
* How could Mohammed Haydar Zammar, a Syrian-born citizen of Germany, have safely recruited the Hamburg pilots when he was under investigation as a possible Al Qaeda operative?
Zammar was under surveillance that included having his telephones tapped at the very time he was to have been recruiting the pilots. At one point, American attempts to learn more about Zammar became so disruptive that German officials threatened to throw an American spy out of the country. The Germans nonetheless passed a steady stream of intelligence about Zammar to the Americans. The Islamist scene in Germany was so active throughout the 1990s that, in addition to the Germans and the Americans, intelligence operatives from Syria, Morocco and other Arab governments kept watch on it.
