First of two parts.

Less than a mile from the mournful place in Lower Manhattan where the World Trade Center came crashing to the ground, in a hushed federal courthouse, a small band of Philadelphia lawyers is prying loose secrets of the Sept. 11, 2001, terror attacks.

It is here that the Cozen O'Connor law firm has filed an 812-page lawsuit on behalf of U.S. and global insurance companies alleging that Saudi Arabia and Saudi-backed Islamist charities nurtured and financed al-Qaeda, the author of those deadly attacks.

Led by its flinty chairman and founder, Stephen Cozen, the firm has invested thousands of hours and millions of dollars to scour the world for witnesses, documents and other evidence in its attempt to hold the oil-rich desert kingdom liable for more than $5 billion in damages.

Among the companies represented in the lawsuit are Chubb, Ace, Allstate, One Beacon, and nearly three dozen other insurers.

"Our concern was whether there was a viable case to be made against the defendant," Cozen said, "and whether the defendant could pay."

Round 1 in this titanic legal battle went to the Saudis and their high-powered lawyers three years ago when a U.S. District Court judge removed the government and Saudi royals as defendants.

Defense lawyers have declined repeated requests for interviews, citing the pending litigation. But in court papers, they describe Cozen's allegations as "fabrications" and note that the 9/11 Commission found no evidence of official Saudi involvement. Moreover, they point out that Saudi Arabia itself has been an al-Qaeda target.

"The showing that the plaintiffs purport to make is complete and utter garbage," said Michael Kellogg, a top Washington appeals lawyer representing Saudi Arabia and members of the royal family, during an appeals argument in January. "It is a collection of newspaper articles, and reports and press releases that show at most the kingdom exercises some supervisory control over the charities."

But Cozen argued that the kingdom and its officials should be restored as defendants. A fiercely competitive lawyer who built a tiny practice into one of the world's leading law firms for insurers, Cozen, 67, contended that the defendants "knew and intended to support al-Qaeda through these charities."

With a ruling from the U.S. Court of Appeals for the Second Circuit imminent, Cozen and his partners have unearthed facts and made connections missed not only by the 9/11 Commission but also by Congress in its investigations.

At the heart of the suit, the biggest and most complex legal action ever undertaken by the law firm, are warnings from U.S. and European officials that the charities were serving as terror fronts.

Among the suit's key assertions:

Senior Saudi officials and members of the royal family or their representatives served as executives or board members of the suspect charities when they were financing al-Qaeda operations. Overall, the Saudi government substantially controlled and financed the charities, the lawsuit alleges.

The charities laundered millions of dollars, some from the Saudi government, into al-Qaeda and other terrorist groups and provided weapons, false travel and employment documents, and safe houses.

Regional offices of the charities employed, in senior positions, al-Qaeda operatives who helped coordinate support for terror cells.

Although the lawsuit argues that the Saudi government "intended" the 9/11 attacks to happen, the public record supporting that allegation is thin, and lawyers suing the kingdom have yet to generate direct evidence that any senior Saudi official conspired with al-Qaeda to attack the United States.

Instead, the lawsuit compiles hundreds of incremental disclosures from U.S government and other sources and weaves them together to form one basic assertion: Al-Qaeda's development from ragtag regional terrorists into a global threat was fueled by Saudi money, some of it from the government.

And the charities, the lawsuit contends, were the money's conduit.

With the help of charities affiliated with the Saudi government, the lawsuit contends, al-Qaeda spread to the vicious 1990s Balkans war, which pitted indigenous Muslims, their al-Qaeda allies, and other mujaheddin against Serbs and Croats.