The Justice Department announced yesterday that the CIA had destroyed 92 videotapes from the agency’s interrogations of high-ranking captured Al Qaeda suspects. In the case of one, Abu Zubaydah, that should not be surprising, because as one American intelligence source has told me, what Zubaydah says on those tapes is the “Rosetta Stone” of what really happened behind the 9/11 terror attacks.

In a short monologue that one investigator told me was the “Rosetta Stone” of 9/11, Zubaydah laid out details of how he and the al Qaeda hierarchy had been supported at high levels inside the Saudi and Pakistan governments.

In my 2003 book, Why America Slept: The Failure to Prevent 9/11, I set forth how Zubaydah initially refused to help his American captors. I also disclosed how US intelligence established a "fake flag" operation, in which the wounded Zubaydah was transferred to Afghanistan under the ruse that he had actually been turned over to the Saudis. The Saudis had him on a wanted list, and the Americans believed that Zubaydah, fearful of torture and death at the hands of the Saudis, would start talking when confronted by US agents playing the role of Saudi intelligence officers.

But when confronted by his "Saudi" interrogators, Zubaydah showed no fear. Instead, according to the two US intelligence sources that provided me the details, he seemed relieved. The man who had been reluctant to even confirm his identity to his US captors suddenly talked animatedly. He was happy to see them, he said, because he feared the Americans would kill him. He then asked his interrogators to call a senior member of the Saudi royal family. And Zubaydah provided a private home number and a cellphone number from memory. "He will tell you what to do," Zubaydah assured them

That man was Prince Ahmed bin Salman bin Abdul-Aziz, one of King Fahd's nephews, and the chairman of the largest Saudi publishing empire. Later, American investigators would determine that Prince Ahmed had been in the US on 9/11.

American interrogators used painkillers to induce Zubaydah to talk—they gave him the meds when he cooperated, and withdrew them when he was quiet. They also utilized a thiopental sodium drip (a so-called truth serum). Several hours after he first fingered Prince Ahmed, his captors challenged the information, and said that since he had disparaged the Saudi royal family, he would be executed. It was at that point that some of the secrets of 9/11 came pouring out. In a short monologue that one investigator told me was the "Rosetta Stone" of 9/11, Zubaydah laid out details of how he and the al Qaeda hierarchy had been supported at high levels inside the Saudi and Pakistan governments.

He named two other Saudi princes, and also the chief of Pakistan's air force, as his major contacts. Moreover, he stunned his interrogators by charging that two of the men, the king's nephew and the Pakistani air-force chief, knew a major terror operation was planned for America on 9/11.

It would be nice to further investigate the men named by Zubaydah, but that is not possible. All four identified by Zubaydah are now dead. As for the three Saudi princes, the king's 43-year-old nephew, Prince Ahmed, died of either a heart attack or blood clot, depending on which report you believe, after having liposuction in Riyadh's top hospital. The second, 41-year-old Prince Sultan bin Faisal bin Turki al-Saud, died the following day in a one-car accident, on his way to the funeral of Prince Ahmed. And one week later, the third Saudi prince named by Zubaydah, 25-year-old Prince Fahd bin Turki bin Saud al-Kabir, died, according to the Saudi Royal Court, "of thirst." The head of Pakistan's air force, Mushaf Ali Mir, was the last to go. He died, together with his wife and 15 of his top aides, when his plane blew up—suspected as sabotage—in February 2003. Pakistan's investigation of the explosion—if one was even done—has never been made public.

Zubaydah is the only top al Queda operative who has secretly linked two of America's closest allies in the war on terror—Saudi Arabia and Pakistan—to the 9/11 attacks. George W. Bush protected the Saudi royal family and the Pakistani military from the implications of Zubaydah's confessions. Bush, because of getting bogged down in Iraq, desperately needed Pakistani and Saudi help. He wanted them to keep Afghanistan from spinning completely out of control, and act as counterweights to the growing power of Iran. The Sunni governments in Riyadh and Islamabad have as much to fear from a resurgent Iran as does any American administration.

But that accommodation meant that the leads about the origins of 9/11 were not pursued. I hoped that President Obama would not be so craven as President Bush in chasing the truth about 9/11, no matter where it leads. Now, with the destruction of the tapes, his intelligence advisers will tell him there was no such thing as the Zubaydah confession.

The American public deserves no less than the complete truth about 9/11. And those CIA officials complicit in hiding the truth by destroying key evidence should be held responsible. President Obama is our last chance.

Gerald Posner is the award-winning author of 10 best-selling books of investigative nonfiction ranging from political assassinations, to Nazi war criminals, to 9/11, to terrorism ( www.posner.com). He also has written dozens of articles for national magazines and newspapers.