Absent financial support from the charities, some of it Saudi government money, they argued, bin Laden would never have been able to pull off 9/11.

At the same time, they pushed forward on their investigation, combing through files and querying defendants. One of those was a major al-Qaeda operative, founder and financier named Wa'el Julaidan. The U.S. Treasury Department designated Julaidan a terrorism financier in 2002.

But Julaidan, responding to Cozen questioning, said the government of Saudi Arabia had subjected him to no penalties or sanctions.

His response mirrored statements by U.S. officials, most recently Stuart Levey, Treasury undersecretary for international terrorism, who said last year that he was unaware of any Saudi sanctions imposed on terrorism financiers living in Saudi Arabia.

During this period, Cozen also learned that at least two Guantanamo Bay detainees had been employees of the Saudi High Commission for Relief of Bosnia and Herzegovina, a Saudi government charity founded and run by Saudi Prince Salman.

In its hearings on whether detainees should be released, the Pentagon considers past employment by the commission and other charities to be a reason for keeping a prisoner in custody.

Cozen also fought a rear-guard action against the U.S. government, seeking to force it to open more investigative files on the charities.

In April 2006, the firm sued the Treasury Department in federal District Court in Philadelphia, alleging it had improperly redacted or withheld thousands of internal documents on the government of Saudi Arabia, the charities, and al-Qaeda that Cozen was seeking.

Cozen appealed Casey's dismissal of the Saudis as defendants on Jan. 5, 2007, attempting to keep them and their resources in the suit. The suit and its ambitions rested on a decision by a three-judge panel of the U.S. Court of Appeals for the Second Circuit in Manhattan.

Cozen's brief argued that the Foreign Sovereign Immunities Act did not protect governments that failed to act when informed that their own agencies promoted terror.

Over the ensuing months, Cozen lawyers continued their investigation and honed their legal arguments. They pursued discovery against defendants who remained in the case, querying them on their business interests and affiliations while jockeying with defense attorneys over the terms of discovery.

A year later, on Jan. 18, the Second Circuit heard arguments.

Stephen Cozen himself was the lead lawyer for the plaintiffs. Flanked by members of his legal team, he stood to make their case.

The Saudi government and members of the royal family, he said, engaged in conduct that breached the standards of normal government activities when they supported Islamist charities that funded extremist groups. In acting outside those standards, they made themselves liable under the law.

Defense lawyer Michael Kellogg answered the allegation. U.S. law afforded the Saudi government substantial protection from litigation, he told the judges. Moreover, there was no evidence that the kingdom had anything to do with the 9/11 attacks, and such evidence was necessary to restore the government and royal family as defendants.

On the surface, at least, the Second Circuit's judges appeared sympathetic to aspects of Cozen's case.

When Kellogg described the close relationship between the kingdom and the United States, the appellate court's chief judge, Dennis Jacobs, cut him short.

"It's neither here nor there," Jacobs said.

The judges posed no question to Cozen, who had been ready for this moment for weeks.