A Brooklyn jury's verdict holding a Jordanian bank liable for Hamas terrorist attacks, combined with a federal appeals court's reinstatement of a similar lawsuit against National Westminster Bank, is ratting international banking as well as policymakers at the U.S. State Dept. In both cases U.S. courts rejected traditional deference to foreign laws and sovereign immunity and showed a willingness to apply American tort law to overseas terrorist attacks.

Now another lawsuit that most observers had written off for dead is showing new signs of life, as plaintiffs including a number of insurance companies file new allegations against the Kingdom of Saudi Arabia for its alleged role in supporting the 9/11 hijackers.

There are still big barriers to suing a sovereign nation in U.S. courts, including the opposition of the federal government. But firms including Motley Rice, the firm that helped win the Arab Bank case and in the 1990s broke down the legal walls protecting the tobacco industry, have convinced an appeals court in New York to allow their case against Saudi Arabia to proceed despite that nation’s strong protests it bears no blame for the terrorist attack that killed more than 2,000 Americans.

In an amended complaint filed in federal court in New York last week, lawyers for the insurance companies and individual plaintiffs argue Saudi Arabia provided direct logistical and financial support to the 9/11 terrorists, 15 of whom were Saudi citizens, through charities it controlled and undercover operatives working in the U.S. To bolster the argument that this case involves U.S. plaintiffs suing over torts committed on U.S. soil, lawyers detail a series of suspicious contacts between Saudi agents and Al Qaeda including Omar Bayoumi, who allegedly held a do-nothing job with a a Saudi aviation firm called Dallah Avco and helped support 9/11 hijackers in San Diego.

“Liability I can prove. Damages I can prove,” said Jerry Goldman, an attorney with Anderson Kill in Philadelphia and New York who represents the family of former World Trade Center Security Director John O’Neill, who was killed in the attack. “It’s a question of whether or not the courts can adjudicate these kinds of claims.”

The Saudi government says it is exempt under the federal Foreign Sovereign Immunities Act, which prohibits most lawsuits against foreign governments, especially when they involve “discretionary functions” such as high-level policy decisions. It won dismissal of the cases in 2005 on that basis and the Second Circuit Court of Appeals upheld, but it substituted its own approach based on the idea that a lawsuit over terrorism could only proceed against countries on the official State Department list of terrorist sponsors (Saudi Arabia isn’t). The Second Circuit abandoned that reasoning in another terrorism case in 2011, however, and ordered the 9/11 case back to trial court for reconsideration last December. The U.S. Supreme Court refused to hear Saudi Arabia’s appeal of that decision in June.

The U.S. government opposed the plaintiffs when they sought Supreme Court review of the first rejection of their case, saying: "Wrongs perpetrated by foreign sovereigns generally have been recognized as appropriate `for diplomatic, rather than legal,' resolution." The plaintiffs also must convince Judge George B. Daniels that the FSIA doesn’t preclude them from suing. Final responses to this latest round of filings are due in mid-November.

Ironically, the better the case they make against the Saudi government, the stronger the discretionary-function argument for dismissal. The law exempts high-level government decisions to avoid sparking international conflict and complicating U.S. foreign relations, said Curtis Bradley, a professor at Duke Law School and expert on sovereign immunity.

“Put aside whether the allegations are true,” Bradley told me. “If they are true, they involve decisions about how to set up charities, how to spend money -- not just low level-individual acts but much more high-level decisions within the Saudi government that cannot be sued upon.”

The plaintiffs might draw some hope from the fact that Daniels, in a December 2011 decision, ordered Iran to pay $6.6 billion in damages for assisting 9/11 terrorists. It was a default judgment because Iran declined to mount a defense, however, and as a State Department-designated sponsor of terrorism, Iran did not have the same defenses as Saudi Arabia. And plaintiffs are running against a strong trend at the Supreme Court toward closing the doors of U.S. courts for lawsuits over foreign torts committed by foreign entities. Well-publicized fiascos like Steven Donziger's crusade to hold Chevron liable for pollution in the Ecuadorian jungle, and aggressive counteractions like an Alabama coal company's pursuit of lawyers suing it over human-rights abuses in Colombia, have discouraged lawyers from filing such suits.

Still, the facts in the Iran case are compelling evidence of a government's involvement in the 9/11 plot. Daniels found that Iranian officials had helped 9/11 hijackers by instructing border guards not to stamp their passports as they traveled through Iran into Afghanistan, making it easier for them to obtain U.S. visas. (Ramzi Bialshibh couldn’t obtain a U.S. visa, the court said, but he used a tourist visa issued by the Iranian embassy in Berlin to travel through Iran to a meeting with al Qaeda leaders in Afghanistan eight months before the attacks.)

Plaintiffs in the New York case accuse Saudi Arabia of providing similar support. “The success of al Qaeda’s jihadist campaign, including the September 11th Attacks themselves, was made possible by the lavish sponsorship al Qaeda received from its material sponsors and supporters, including the Kingdom” of Saudi Arabia, they say, “over more than a decade leading up to September 11, 2001.” Al Qaeda took advantage of an existing network of Saudi charities that were funded the holy war against Russian occupiers in Afghanistan and later backed Muslim warriers in Bosnia, the complaint says, to raise $30 million a year.

Facing attacks on its legitimacy at home, the Saudi regime established Islamic Affairs Departments in its embassies around the world to spread its fundamentalist Wahhabi faith and funnel contributions to charities supporting extremist ideologies, the complaint says.

The lawyers accuse Bayoumi of working with Islamic Affairs to support hijackers Nawaf al Hazmi and Khalid al Mihdhar after they arrived in Los Angeles in 2000. Bayoumi was living in San Diego on a $3,000-a-month stipend issued by Dallah Avco, which was owned by a wealthy Saudi backer of Al Qaeda, but Dallah Avco has said Bayoumi was actually an employee of the Saudi government the whole time. Investigators later concluded that Bayoumi traveled to Los Angeles to meet with Fahad al Thumairy, a Saudi official in the Islamic Affairs office there, where they “discussed the recent arrival of future 9/11 hijackers.” Bayoumi found the men an apartment and opened a bank account for them using his own money, the complaint says. He and Thumairy exchanged a number of phone calls before the attacks, and Thumairy was expelled for alleged terrorist links in 2003.

The complaint also accuses Bayoumi of introducing the hijackers to Anwar Aulaqi, the American cleric who was killed in a 2011 drone strike in Yemen. Aulaqi and associates helped the hijackers obtain housing and flight lessons, the complaint says. Likewise, Saleh Ibn Abdul Rahman Hussayen, described as a former Saudi official and senior member of the Ulema, or conservative religious movement, appeared in the U.S. shortly before the attacks and moved into the same Virginia hotel where the hijackers were staying days before 9/11. The Second Circuit Court of Appeals later concluded that his suspicious movements “raise a plausible inference” he was assisting the hijackers on U.S. soil.

In March 2002, the complaint says, King Fahd bin Adbul Aziz al Saud appointed Hussayen as the President of the Committee of the Two Holy Mosques in Mecca and Medina, the two most sacred sites in Islam. He is now dead.

With all this evidence, the lawyers hope to convince Daniels to allow them to proceed to discovery. Mark Hansen, a partner with Kellogg , Huber, Hansen, Todd, Evans & Figel in Washington who represents the Saudi government, said it is firm policy not to comment on pending litigation. In its motion to dismiss the case yet again, however, the kingdom says “Saudi Arabia had no role in the attacks of September 11, 2001.”

“The United States has said often and vigorously that Saudi Arabia is an important ally in the fight against terrorism,” the motion says. “The National Commission on Terrorist Attacks Upon the United States (the“9/11 Commission”) found `no evidence’ in 2004 that `the Saudi government as an institution or senior Saudi officials individually funded’ the September 11 terrorists or their al Qaeda organization.”

Plaintiff lawyers argue the evidence shows Saudi officials, at some level, provided meaningful support to the terrorists. They also argue the exception for discretionary acts doesn’t apply under a 1980 precedent set by the federal court that allowed a civil suit against the Pinochet government of Chile for its murder of Orlando Letelier, a leftist activist, along with an American colleague in Washington in 1976.

“I’m sure the Pinochet government thought that was a policy-level decision that was in their interests,” said Sean Carter, an attorney with Cozen O’Conner who is chair of the plaintiffs’ executive committee and represents the insurance companies suing Saudi Arabia for billions of dollars in claims paid over the World Trade Center collapse. “But there are limits.”

Bradley of Duke Law said the plaintiffs would be better off if they could show Saudi officials were actually at the controls of the doomed airliners, rather than Saudi citizens who may have been supported by government-sponsored charities. It’s harder for the court to draw a line between legal policy decisions that wind up looking terrible in hindsight, and premeditated murder, he said.

“What’s the benefit of immunity if you only get it when you’re acting well?” Bradley asked.

Goldman is confident he can convince the judge to allow his case to proceed this time. The tort exception to the FSIA, he said, isn’t just a side door the plaintiffs can use to drag Saudi Arabia into a U.S. court.

“This is the royal entryway,” he said. “The gates to the palace are open.”

That remains to be seen. The case is an important test of the project plaintiff lawyers have mounted, with the help of like-minded members of Congress, to turn U.S. courts into a tool for fighting terrorism worldwide.

“We’d like to find out who did this,” Goldman said. “And we’d like to use the legal system to discourage people from doing it again. It’s deterrence.”