It’s easier to bury uncomfortable facts than to confront them. So this September 11, the ceremonies marking the 2001 attacks on New York and Washington, D.C., will simply honor the dead. In Manhattan, tourists and mourners will gather where the World Trade Center Towers once stood, lowering their heads in memory of the 2,606 who perished there. The services won't reflect the view that the attacks might well have been prevented.

But for hundreds of families and a growing number of former FBI agents, the grief of another 9/11 ceremony will be laced with barely muted rage: There remains a conspiracy of silence among high former U.S. and Saudi officials about the attacks.

“It’s horrible. We still don’t know what happened,” said Ali Soufan, one of the lead FBI counterterrorism agents whom the CIA kept in the dark about the movements of the future Al-Qaeda hijackers. To Soufan and many other former national security officials, the unanswered questions about the events leading up to the September 11, 2001, attacks dwarf those about the assassination of John F. Kennedy, because “9/11 changed the whole world.” It not only led to the invasions of Afghanistan and Iraq, the fracturing of the Middle East and the global growth of Islamic militantism but also pushed the U.S. closer to being a virtual homeland-security police state.

“I am sad and depressed about it,” said Mark Rossini, one of two FBI agents assigned to the CIA’s Osama bin Laden unit, who says agency managers mysteriously blocked them from informing their headquarters about future Al-Qaeda plotters present in the United States in 2000 and again in the summer of 2001. “It is patently evident the attacks did not need to happen and there has been no justice,” he said.

The authors of a new book on 9/11 hope to refocus public attention on the cover-up. Thoroughly mining the multiple official investigations into the event, John Duffy and Ray Nowosielski find huge holes and contradictions in the official story that 9/11 was merely “a failure to connect the dots.”

Duffy, a left-leaning writer and environmental activist, and Nowosielski, a documentary filmmaker, have nowhere near the prominence of other journalists who have poked holes in the official story, in particular Lawrence Wright, author of The Looming Tower: Al-Qaeda and the Road to 9/11, the Pulitzer Prize–winning book that was turned into a gripping multi-part docudrama on Hulu earlier this year.

But Duffy and Nowosielski come to the story with a noteworthy credential: In 2009 they scored an astounding video interview with Richard Clarke, a White House counterterrorism adviser during the Bill Clinton and George W. Bush administrations. In it, Clarke raged that top CIA officials, including director George Tenet, had withheld crucial information from him about Al-Qaeda’s plotting and movements, including the arrival in the U.S. of future hijackers Khalid al-Mihdhar and Nawaf al-Hazmi. In The Watchdogs Didn’t Bark: The CIA, NSA, and the Crimes of the War on Terror, the authors assemble a compelling case of a government-wide cover-up of Saudi complicity in the affair.

In 2002, Tenet swore to Congress that he wasn’t aware of the imminent threat because it came in a cable that wasn’t marked urgent—and “no one read it.” But his story was shredded five years later when Senators Ron Wyden and Kit Bond forced loose an executive summary of the CIA’s own internal investigation of 9/11, which stated that “some 50 to 60 individuals read one or more of the six Agency cables containing travel information related to these terrorists.”

Clarke went ballistic. Until then, he had trusted Tenet, a close colleague and friend, to tell the truth. In 2009, despairing at the lack of media traction on the astounding disclosure, he wrote a book about the duplicity, Your Government Failed You, which was largely ignored. So when Duffy and Nowosielski came calling, he welcomed them.

“I believed, for the longest time, that this was one or two low-level desk officers who got this [information about Hazmi and Mihdhar] and somehow didn’t realize the significance,” he told them. But “50—five oh—50 CIA officers knew this, and they included [Tenet and] all kinds of people who were regularly talking to me? Saying I’m pissed doesn’t begin to describe it.”

All these years later, it’s still unclear why the CIA would keep such crucial details about Al-Qaeda movements from the FBI. Clarke and other insiders suspect that the spy agency had a deeply compartmented plan in the works to recruit Hazmi, Mihdhar and perhaps other Al-Qaeda operatives as double agents. If the FBI discovered they were in California, the theory goes, it would have demanded their arrest. When the CIA’s recruitment ploy fizzled, Tenet and company hid the details from Clarke lest they be accused of “malfeasance and misfeasance,” he said.

It’s the only logical explanation for why the presence of Hazmi and Mihdhar was kept from him until after the attacks, Clarke said. “They told us everything—except this,” he says in the video.

Tenet and two of his counterterrorism deputies, Rich Blee and Cofer Black, issued a statement calling Clarke’s theory “reckless and profoundly wrong.” But now Clarke has company. Duffy and Nowosielski found other key former FBI counterterrorism agents and officials who have developed deep doubts about Tenet’s story. The only element they disagree on is which officials were responsible for the alleged subterfuge.

“I think if there were some conscious effort” not to tell the bureau what was going on, Dale Watson, a former FBI deputy chief of counterterrorism told them, “it was probably” carried out below Tenet, Blee and Black, by managers of the CIA’s Osama bin Laden unit.

But Pat D’Amuro, an even more senior former FBI counterterrorism official, told them, “There’s no doubt in my mind that [withholding the information] went up further in the agency” than those managers. “And why they didn’t send it over, to this day, I don’t know why.”

And then there’s the continuing mystery of Saudi complicity with the hijackers. Duffy and Nowosielski offer a tightly focused update on what’s been learned about Saudi support for Al-Qaeda in recent years. Back in 2004, the official 9/11 Commission said it found no evidence that the “Saudi government as an institution, or senior Saudi officials individually funded” Al-Qaeda.

A year later, the highly redacted CIA inspector general’s report cracked open another window, saying that some agency officers had “speculated” that “dissident sympathizers within the government” (i.e., religious extremists) may have supported bin Laden. Subsequent investigations have revealed that officials from the kingdom’s Islamic affairs ministry were actively helping the hijackers get settled in California.

Such information spurred several hundred families of the 9/11 attack victims to file suit against the Saudi government in federal court in New York last year, seeking unspecified monetary damages.

“Saudi intelligence has admitted that they knew who these two guys were,” Andrew Maloney, an attorney for families, told Newsweek last week. “They knew they were Al-Qaeda the day they arrived in Los Angeles. So any notion from the Saudi government saying, ‘Oh, we just help out all Saudis here’ is false. They knew. And the CIA knew.”

The kingdom has turned over some 6,800 pages of documents, “mostly in Arabic,” that Maloney’s team is in the process of translating. “There’s some interesting things in there,” he said, “and some clear gaps.” He said he’ll return to court in October to press for more documents.

He also wants to depose Saudi officials, particularly Fahad al-Thumairy, a former Los Angeles consular official and imam of a Culver City, California, mosque attended by the hijackers. In 2003, Thumairy was intercepted after he landed in Los Angeles on a flight from Germany and deported from the U.S. “because of suspected terrorist links.” But he still works for the government in Riyadh, Maloney said. “Can you believe that?”

In April, Maloney subpoenaed the FBI for documents on Thumairy and Omar al-Bayoumi, a suspected Saudi spy in the U.S. who was also in contact with the hijackers. The bureau has not responded, so on September 11 he plans to file “a formal motion to compel the FBI” to produce the documents. His motion follows a sworn statement by Steven Moore, the FBI agent who headed the bureau’s investigation into the hijacking of the plane that flew into the Pentagon, charging the 9/11 Commission with misleading the public when it said it “had not found evidence” of Saudi assistance to Hazmi and Mihdhar.

“There was clearly evidence that Thumairy provided assistance to Hazmi and Mihdhar,” Moore wrote. And “based on the proof in our investigation,” he added, “Bayoumi himself was a clandestine agent and associated with radical extremists, including Thumairy.”

Moore’s statement was first reported by the Florida Bulldog, a Fort Lauderdale news site that has been investigating the hijackers’ contacts with flight schools. “To my knowledge,” Moore stated, “Thumairy has never been the subject of a genuine law enforcement interview conducted by the actual agents who investigated him.”

Maloney’s additional targets are other FBI, CIA, State Department and Treasury Department personnel and documents. “There are a lot of people, former agents—I won't identify who or what agencies—who have talked to us,” he said, but others, especially in the CIA’s bin Laden unit, “will never talk to us or will only talk to us if they are given some kind of blanket immunity.”  

Getting access to them, he said, would probably require an executive order from President Donald Trump—an unlikely outcome given his administration’s strong backing for the Saudi monarchy.

There may be public support for Maloney’s endeavors. A 2016 poll found a slight majority of Americans (54.3 percent) believe that the government is hiding something about the 9/11 attacks. Then again, a considerable number of 9/11 "truthers" embrace conspiracy theories positing that the attacks were “an inside job” by the Bush administration and/or Israel and abetted by explosives planted in one of the World Trade Center towers.

But they are right about Saudi resistance to fully disclosing its relations with the hijackers. Last year, agents of the monarchy were discovered surreptitiously funding a PR effort to derail a congressional bill permitting a 9/11 families group to sue the kingdom for damages. Last September, the family group filed a 17-page complaint with the Justice Department.

Terry Strada, a leader of the group 9/11 Families & Survivors United for Justice Against Terrorism, will mourn again this year, but not at the site where the towers once stood and her husband died. She plans to attend “a private service” at the Shrine of St. Joseph in Stirling, New Jersey, which she said has “a beautiful and solemn space” dedicated to all who died in the 9/11 attacks.

But she is also full of fury at the government’s refusal to release all it knows about the run-up to the attacks. “It’s very sad that we’re still being kept in the dark about it. It’s frustrating. It angers me,” she told Newsweek. “It’s a slap in the face. They think they’re above the law and don’t have to respond to the families—and the world. It’s disgusting.”

But Strada evinces even more disdain for the Saudis. Responding to Secretary of State Mike Pompeo’s August 20 message “wishing Muslims around the world a blessed Eid al-Adha,” she tweeted, “Seriously???”

Strada added, “The Saudis promote & finance the most virulent hatred toward Americans than any other nation. Murdered 3,000 on Sept 11.” The “9/11 families,” she wrote, “will #NEVERFORGET. #FreeTheTruth”

Correction: An earlier version of this story gave an incorrect subtitle for John Duffy and Ray Nowosielski’s new book, The Watchdogs Didn’t Bark: The CIA, NSA, and the Crimes of the War on Terror.