WASHINGTON >> Saudi Arabia paid millions of dollars to Washington lobbyists to keep it out of court. They have been unsuccessful. And now it is up to the kingdom’s lawyers to limit the damage.

With families of Sept. 11 victims now able to pursue legal claims against the Saudis, the fight over responsibility for the terrorist attacks 15 years ago is likely to shift to a courtroom in Lower Manhattan, not far from where the World Trade Center once stood.

The legal battle could last for years, and would be waged using thousands of pages of documents, deposition transcripts and official government investigations. It could end in millions — or billions — of dollars’ worth of Saudi assets being seized in a court settlement, or a judgment that largely vindicates the Saudi government, which for years has insisted it had no role in the deadly plot.

Lawyers for both sides were shaping a legal strategy Thursday, the day after Congress overrode a veto of a law allowing the 9/11 suits to go forward. For more than a decade, they have been blunted by a sovereign immunity law protecting foreign governments from U.S. lawsuits.

Now, lawyers say they expect that a federal judge will once again take up the cases originally filed in courtrooms across America, but that several years ago were consolidated into one suit in the Southern District of New York.

In recent months, the Saudi government used a constellation of Washington lobbying and public relations firms to try to thwart the Sept. 11 bill as it made its way through Congress, a clear sign of the angst in the Saudi capital of Riyadh over the legislation’s long-term implications.

But despite the congressional drama, the angry barbs from Obama and warnings from Saudi officials that they may need to sell off hundreds of millions of dollars’ worth of assets to avoid their being seized in a court settlement, some legal experts said that the 9/11 plaintiffs face a headwind in trying to prove Saudi involvement.

“Although there is loose talk of 10 billion dollars’ worth of judgments against Saudi Arabia, in fact the deck remains stacked against the plaintiffs,” said Raj Bhala, a professor of international and comparative law at the University of Kansas Law School.

The most significant hurdle facing the roughly 9,000 plaintiffs, a combination of family members of people killed in the Sept. 11 attacks and people injured on that day, is to persuade a court there is solid evidence of a direct Saudi government role in the attacks.

The U.S. government — from the FBI to the 9/11 Commission to a separate congressional inquiry — has spent years and millions of dollars investigating the attacks and thus far has not found proof that Saudi officials were complicit in the plot.

The 9/11 Commission found “no evidence that the Saudi government as an institution or senior Saudi officials individually funded” al-Qaida. But the commission’s phrasing left some to speculate that there might be evidence of involvement by other, lower-ranking officials.

Some investigators have long thought that the various inquiries never unearthed the truth about several individuals connected to the Saudi government at the time of the attack, in particular a Saudi consular official in Los Angeles named Fahad al-Thumairy.

Thumairy, who had been the imam at the King Fahd Mosque in Culver City, Calif., had contact with two of the hijackers — Nawaf al-Hazmi and Khalid al-Mihdhar — in the months before the attacks. An FBI document in 2012 concluded that he had assigned someone to take care of the two men during their time in the Los Angeles area.

Another Saudi who was on the kingdom’s payroll at the time, Omar al-Bayoumi, later helped the two men settle in San Diego. Both Thumairy and Bayoumi vigorously denied to U.S. investigators that they had knowingly assisted in the terrorist plot.

But the exact roles of the two men, and potentially the roles of other Saudi officials, could be closely scrutinized in the months and years ahead. Sean Carter, one of the lead lawyers for the plaintiffs in the case in the Southern District, said that his team’s 156-page complaint alleging a Saudi government role in the attacks was buttressed by 4,500 pages of supporting evidence.

The new law, Carter said, could open the way for new discovery in the case and even to depositions of Thumairy and other Saudi citizens.

But Eric Lewis, a lawyer for two Saudi charities that have been defendants in the continuing Sept. 11 litigation, said that lawyers for the plaintiffs would not be able to use the discovery process as a fishing expedition to depose any Saudi citizen they thought could be tangentially connected to the case. They would have to convince the judge, he said, that the Saudi government was still directly responsible for Thumairy or anyone else the plaintiffs would like to depose.

Lewis said that “there is no there there” on the allegations of any Saudi government role in the attacks, given the kingdom’s long history of being at war with al-Qaida.

“The notion that senior Saudi officials or the Saudi government had an interest in supporting Sept. 11 and the attack on the World Trade Center is patently absurd,” he said.

Obama administration officials have warned for months that the Sept. 11 bill sets a dangerous precedent and could lead other nations to retaliate, possibly exposing the United States to private lawsuits in foreign courts because of U.S. intelligence or military operations overseas. On Thursday, several members of Congress who voted for the law acknowledged that it might need to be amended.

Officials and analysts across the Persian Gulf responded angrily on Thursday to the bill’s passage, and said it had led their countries to begin rethinking their alliance with the United States. Some suggested that Saudi Arabia and its regional allies had ways of striking back at what they saw as a betrayal by the United States, by lessening their investments in the United States or dialing back their engagement in joint military and security programs. Others said that the bill would make Saudi investors less comfortable putting their money in the United States.

Saudi Arabia’s Ministry of Foreign Affairs issued a statement saying that “the erosion of sovereign immunity will have a negative impact on all nations, including the United States” and raised the prospect that Congress might take new action during the lame-duck session in November that might blunt the effect of the bill.

“It is our hope that wisdom will prevail and the Congress will take the necessary steps to correct this legislation in order to avoid the serious unintended consequences that may ensue,” it said.

Some opponents of the new law, both in the United States and overseas, said they hoped that the Obama administration would eventually make use of the legislation’s provisions allowing the attorney general to intervene directly in the civil court proceedings — effectively to delay proceedings if the government could convince a judge that the United States and Saudi Arabia are in discussions to settle the cases outside of court.

Starting any discussions — even as a delay tactic — would take some convincing for Saudi officials. The kingdom, said Bhala, the law professor at the University of Kansas, “has said that going down the road of settlement negotiations would be tantamount to an admission of guilt.”

But, Bhala added, “They could see things differently now.”

© 2016 The New York Times Company