Even al-Qaeda had $8 million in frozen assets that plaintiffs could seize if they won.

In the end, Cozen said, it was the legal simplicity of the case that seemed most persuasive - and a huge payout if they succeeded.

Although the question of who financed the movement that carried out the 9/11 attacks involved complex fact patterns and difficult investigative hurdles, the legal theory behind the case wasn't terribly different from the subrogation work the firm had made a specialty: Look for people or businesses responsible for a loss and make them pay.

Seeking damages from Saudi Arabia was, in its essence, no different from going after any business, contractor or third party for liability.

"It was our very strong recommendation to our clients," Cozen said, "that the case be pursued."

Then came the hard part.

Funding the lawsuit

Through their own investigation, Cozen lawyers learned that a major money-center bank (one that participates in national and international money markets) in the United States, which Cozen declined to identify, was planning to purchase a smaller bank. Evidence suggested that the smaller bank had served as a conduit for financial transactions of extremist groups.

With that information in hand, Cozen lawyers approached the money-center bank. To avoid being named as a defendant, it settled for millions of dollars, money that was used to offset some of the costs of preparing the lawsuit.

The firm filed its lawsuit on Sept. 10, 2003, naming more than 400 defendants and seeking to recover about $5 billion. Yet that amount far understated what was at stake financially. Because Cozen and other law firms sued under laws that permit plaintiffs to collect treble and punitive damages along with attorneys' fees, the actual award could easily reach the tens of billions of dollars.

Hearing the case was U.S. District Judge Richard Conway Casey, a former prosecutor and a graduate of Holy Cross College and the Georgetown University Law Center.

It was in his Manhattan courtroom that the two sides met for a series of arguments between September and November 2004, when each laid out its position.

Cozen lawyers argued that the Saudis not only had funded and controlled the charities, but had been warned that the charities helped launder money into al-Qaeda. The defense insisted that there was no evidence that the Saudi government had supported acts of terrorism, and that the kingdom itself had been a victim of extremist groups, including al-Qaeda.

In one particularly intense hearing, Casey pushed back hard against Saudi arguments. For a while, Cozen lawyers thought they had been able to convince him.

But only a few weeks later, in January, and then in September, Casey issued two hard-hitting and emphatic rulings. He found the Saudi government immune from being sued because its oversight and financial support for the charities constituted normal government activities.

And he discounted information that the Saudis had been warned about the charities' money-laundering, and cited a 9/11 Commission finding that it had "no evidence that the Saudi government as an institution or senior Saudi officials individually funded" al-Qaeda.

Cozen and associates were outraged. They believed their investigation had gone considerably beyond the work of the 9/11 Commission, by showing that the Saudis had substantial control over the charities, had been warned repeatedly that the charities posed a problem, yet had had taken no actions.

Casey, Cozen felt, had profoundly misconstrued the case by failing to recognize Saudi responsibility.

Cozen lawyers began mapping their appeal.