Anthony Summers and Robynn Swan write:

For 10 years now, a major question about 9/11 has remained unresolved. It was, as 9/11-commission chairmen Thomas Kean and Lee Hamilton recalled, “Had the hijackers received any support from foreign governments?” There was information that pointed to the answer, but the commissioners apparently deemed it too disquieting to share in full with the public.

The idea that al-Qaeda had not acted alone was there from the start. “The terrorists do not function in a vacuum,” Defense Secretary Donald Rumsfeld told reporters the week after 9/11. “I know a lot, and what I have said, as clearly as I know how, is that states are supporting these people.” Pressed to elaborate, Rumsfeld was silent for a long moment. Then, saying it was a sensitive matter, he changed the subject.

Three years later, the commission would consider whether any of three foreign countries in particular might have had a role in the attacks. Two were avowed foes of the United States: Iraq and Iran. The third had long been billed as a close friend: Saudi Arabia.

In its report, the commission stated that it had seen no “evidence indicating that Iraq cooperated with al-Qaeda in developing or carrying out any attacks against the United States.”

Iran, the commission found, had long had contacts with al-Qaeda and had allowed its operatives—including a number of the future hijackers—to travel freely through its airports. Though there was no evidence that Iran “was aware of the planning for what later became the 9/11 attack,” the commissioners called on the government to investigate further.

This year, in late May, attorneys for bereaved 9/11 family members said there was revealing new testimony from three Iranian defectors. Former senior commission counsel Dietrich Snell was quoted as saying in an affidavit that there was now “convincing evidence the government of Iran provided material support to al-Qaeda in the planning and execution of the 9/11 attack.” That evidence, however, has yet to surface.

As for Saudi Arabia, America’s purported friend, you would have thought from the reaction of the Saudi ambassador, Prince Bandar bin Sultan, that the commission had found nothing dubious in his country’s role. “The clear statements by this independent, bipartisan commission,” he declared, “have debunked the myths that have cast fear and doubt over Saudi Arabia.” Yet no finding in the report categorically exonerated Saudi Arabia.

The commission’s decision as to what to say on the subject had been made amid discord and tension. Late one night in 2004, as last-minute changes to the report were being made, investigators who had worked on the Saudi angle received alarming news. Their team leader, Dietrich Snell, was at the office, closeted with executive director Philip Zelikow, making major changes to their material and removing key elements.

The investigators, Michael Jacobson and Rajesh De, hurried to the office to confront Snell. With lawyerly caution, he said he thought there was insufficient substance to their case against the Saudis. They considered the possibility of resigning, then settled for a compromise. Much of the telling information they had collected would survive in the report, but only in tiny print, hidden in the endnotes.