As the 20th anniversary of the Sept. 11 terrorist attacks approaches, victims’ relatives are pressing the courts to answer what they see as lingering questions about the Saudi government’s role.

A lawsuit that accuses Saudi Arabia of being complicit took a major step forward this year with the questioning under oath of former Saudi officials, but those depositions remain under seal and the U.S. has withheld a trove of other documents as too sensitive for disclosure.

The information vacuum has exasperated families who have tried to make the case that the Saudi government facilitated the attacks. Past investigations have outlined ties between Saudi nationals and some of the airplane hijackers, but have not established the government was directly involved.

“The legal team and the FBI, investigative agencies, can know about the details of my dad’s death and thousands of other family members’ deaths, but the people who it’s most relevant to can’t know,” said Brett Eagleson, whose father, Bruce, was among the World Trade Center victims. “It’s adding salt to an open wound for all the 9/11 family members.”

Lawyers for the victims plan to ask a judge to lift a protective order so their clients can access secret government documents as well as testimony from key subjects interviewed over the last year. Though the plaintiffs’ lawyers are unable to discuss what they’ve learned from depositions, they insist the information they’ve gathered advances their premise of Saudi complicity.

“We’re in a situation where only now, through the documents we have gotten and what our investigators have discovered and the testimony we’ve taken, only now is this iceberg that’s been underwater” floating to the surface, said, attorney James Kreindler.

The Saudi government has denied any connection to the attacks. But the question has long vexed investigators and is at the heart of a long-running lawsuit in Manhattan on behalf of thousands of victims. The issue gained traction not only because 15 of the 19 hijackers were Saudi — as was Osama bin Laden, the mastermind — but also because of suspicions they must have had help to navigate Western society given their minimal experience in the U.S.

Public documents released in the last two decades, including by the 9/11 Commission, have detailed numerous Saudi entanglements but have not proved government complicity.

They show how the first hijackers to arrive in the U.S., Nawaf al-Hazmi and Khalid al-Mihdhar, were met and assisted by a Saudi national in 2000. That man, Omar al-Bayoumi, who helped them find and lease an apartment in San Diego, had ties to the Saudi government and had attracted FBI scrutiny, investigators have said.

The commission in 2004 said it found no evidence the Saudi government or senior Saudi officials had funded al-Qaida, though it noted Saudi-linked charities could have diverted money to the group.

The suit gained steam with a judge’s 2018 ruling permitting plaintiffs’ lawyers to do a limited fact-finding investigation.