The following script is from "28 Pages" which aired on April 10, 2016. Steve Kroft is the correspondent. Howard Rosenberg and Julie Holstein, producers.

In 10 days, President Obama will visit Saudi Arabia at a time of deep mistrust between the two allies, and lingering doubts about the Saudi commitment to fighting violent Islamic extremism.

It also comes at a time when the White House and intelligence officials are reviewing whether to declassify one of the country's most sensitive documents -- known as the "28 pages." They have to do with 9/11 and the possible existence of a Saudi support network for the hijackers while they were in the U.S.

For 13 years, the 28 pages have been locked away in a secret vault. Only a small group of people have ever seen them. Tonight, you will hear from some of the people who have read them and believe, along with the families of 9/11 victims that they should be declassified.

Bob Graham: I think it is implausible to believe that 19 people, most of whom didn't speak English, most of whom had never been in the United States before, many of whom didn't have a high school education-- could've carried out such a complicated task without some support from within the United States.

Steve Kroft: And you believe that the 28 pages are crucial to this? Understand...

Bob Graham: I think they are a key part.

Former U.S. Senator Bob Graham has been trying to get the 28 pages released since the day they were classified back in 2003, when he played a major role in the first government investigation into 9/11.

Bob Graham: I remain deeply disturbed by the amount of material that has been censored from this report.

At the time, Graham was chairman of the Senate Select Committee on Intelligence and co-chair of the bipartisan joint congressional inquiry into intelligence failures surrounding the attacks. The Joint Inquiry reviewed a half a million documents, interviewed hundreds of witnesses and produced an 838 page report -- minus the final chapter which was blanked out -- excised by the Bush administration for reasons of national security.

"I remain deeply disturbed by the amount of material that has been censored from this report."

Bob Graham won't discuss the classified information in the 28 pages, he will say only that they outline a network of people that he believes supported the hijackers while they were in the U.S.

Steve Kroft: You believe that support came from Saudi Arabia?

Bob Graham: Substantially.

Steve Kroft: And when we say, "The Saudis," you mean the government, the--

Bob Graham: I mean--

Steve Kroft: --rich people in the country? Charities--

Bob Graham: All of the above.

Graham and others believe the Saudi role has been soft-pedaled to protect a delicate relationship with a complicated kingdom where the rulers, royalty, riches and religion are all deeply intertwined in its institutions.

Bob Graham CBS News

Porter Goss, who was Graham's Republican co-chairman on the House side of the Joint Inquiry, and later director of the CIA, also felt strongly that an uncensored version of the 28 pages should be included in the final report. The two men made their case to the FBI and its then-director Robert Mueller in a face-to-face meeting.

Porter Goss: And they pushed back very hard on the 28 pages and they said, "No, that cannot be unclassified at this time."

Steve Kroft: Did you happen to ask the FBI director why it was classified?

Porter Goss: We did, in a general way, and the answer was because, "We said so and it needs to be classified."

Goss says he knew of no reason then and knows of no reason now why the pages need to be classified. They are locked away under the capital in guarded vaults called Sensitive Compartmented Information Facilities, or SCIFs in government jargon. This is as close as we could get with our cameras -- a highly restricted area where members of Congress with the proper clearances can read the documents under close supervision. No note-taking allowed.

Tim Roemer: It's all gotta go up here, Steve.

Tim Roemer, a former Democratic congressman and U.S. ambassador to India, has read the 28 pages multiple times. First as a member of the Joint Inquiry and later as a member of the blue-ribbon 9/11 Commission which picked up where Congress' investigation left off.

Steve Kroft: How hard is it to actually read these 28 pages?

Tim Roemer: Very hard. These are tough documents to get your eyes on.

Roemer and others who have actually read the 28 pages, describe them as a working draft similar to a grand jury or police report that includes provocative evidence -- some verified, and some not. They lay out the possibility of official Saudi assistance for two of the hijackers who settled in Southern California. That information from the 28-pages was turned over to the 9/11 Commission for further investigation. Some of the questions raised were answered in the commission's final report. Others were not.

Steve Kroft: Is there information in the 28 pages that, if they were declassified, would surprise people?

Tim Roemer: Sure, you're gonna be surprised by it. And, you're going to be surprised by some of the answers that are sitting there today in the 9/11 Commission report about what happened in San Diego, and what happened in Los Angeles. And what was the Saudi involvement.

Much of that surprising information is buried in footnotes and appendices of the 9/11 report -- part of the official public record, but most of it unknown to the general public. These are some, but not all of the facts:

In January of 2000, the first of the hijackers landed in Los Angeles after attending an al Qaeda summit in Kuala Lumpur, Malaysia. The two Saudi nationals, Nawaf al-Hazmi and Khalid al-Mihdhar, arrived with extremely limited language skills and no experience with Western culture. Yet, through an incredible series of circumstances, they managed to get everything they needed, from housing to flight lessons.

Tim Roemer: L.A., San Diego, that's really you know, the hornet's nest. That's really the one that I continue to think about almost on a daily basis.

During their first days in L.A., witnesses place the two future hijackers at the King Fahd mosque in the company of Fahad al-Thumairy, a diplomat at the Saudi consulate known to hold extremist views. Later, 9/11 investigators would find him deceptive and suspicious and in 2003, he would be denied reentry to the United States for having suspected ties to terrorist activity.

Tim Roemer: This is a very interesting person in the whole 9/11 episode of who might've helped whom-- in Los Angeles and San Diego, with two terrorists who didn't know their way around.

Phone records show that Thumairy was also in regular contact with this man: Omar al-Bayoumi, a mysterious Saudi who became the hijackers biggest benefactor. He was a ghost employee with a no-show job at a Saudi aviation contractor outside Los Angeles while drawing a paycheck from the Saudi government.

Steve Kroft: You believe Bayoumi was a Saudi agent?

Bob Graham: Yes, and--

Steve Kroft: What makes you believe that?

Bob Graham: --well, for one thing, he'd been listed even before 9/11 in FBI files as being a Saudi agent.

On the morning of February 1, 2000, Bayoumi went to the office of the Saudi consulate where Thumairy worked. He then proceeded to have lunch at a Middle Eastern restaurant on Venice Boulevard where he later claimed he just happened to make the acquaintance of the two future hijackers.

Tim Roemer: Hazmi and Mihdhar magically run into Bayoumi in a restaurant that Bayoumi claims is a coincidence and in one of the biggest cities in the United States.

Steve Kroft: And he decides to befriend them.

Tim Roemer: He decides to not only befriend them but then to help them move to San Diego and get residence.

In San Diego, Bayoumi found them a place to live in his own apartment complex, advanced them the security deposit and cosigned the lease. He even threw them a party and introduced them to other Muslims who would help the hijackers obtain government IDs and enroll in English classes and flight schools. There's no evidence that Bayoumi or Thumairy knew what the future hijackers were up to, and it is possible that they were just trying to help fellow Muslims.

The very day Bayoumi welcomed the hijackers to San Diego, there were four calls between his cell phone and the imam at a San Diego mosque, Anwar al-Awlaki, a name that should sound familiar.

The American-born Awlaki would be infamous a decade later as al Qaeda's chief propagandist and top operative in Yemen until he was taken out by a CIA drone. But in January 2001, a year after becoming the hijackers' spiritual adviser, he left San Diego for Falls Church, Virginia. Months later Hazmi, Mihdhar and three more hijackers would join him there.

Tim Roemer: Those are a lot of coincidences, and that's a lot of smoke. Is that enough to make you squirm and uncomfortable, and dig harder-- and declassify these 28 pages? Absolutely.

Perhaps, no one is more interested in reading the 28 pages than attorneys Jim Kreindler and Sean Carter who represent family members of the 9/11 victims in their lawsuit against the kingdom. Alleging that its' institutions provided money to al Qaeda knowing that it was waging war against the United States.

Jim Kreindler: What we're doing in court is developing the story that has to come out. But it's been difficult for us because for many years, we weren't getting the kind of openness and cooperation that we think our government owes to the American people, particularly the families of people who were murdered.

The U.S. government has even backed the Saudi position in court--that it can't be sued because it enjoys sovereign immunity. The 9/11 Commission report says that Saudi Arabia has long been considered the primary source of al Qaeda funding through its' wealthy citizens and charities with significant government sponsorship. But the sentence that got the most attention when the report came out is this:

"We have found no evidence that the Saudi government as an institution or senior Saudi officials individually funded the organization."

Attorney Sean carter says it's the most carefully crafted line in the 9/11 Commission report and the most misunderstood.

Sean Carter: When they say they found no evidence that senior Saudi officials individually funded al Qaeda, they conspicuously leave open the potential that they found evidence that people who were officials that they did not regard as senior officials had done so. That is the essence of the families' lawsuit. That elements of the government and lower level officials sympathetic to bin Laden's cause helped al Qaeda carry out the attacks and help sustain the al Qaeda network.

Yet, for more than a decade, the kingdom has maintained that that one sentence exonerated it of any responsibility for 9/11 r­­egardless of what might be in the 28 pages.

Bob Kerrey: It's not an exoneration. What we said--we did not, with this report, exonerate the Saudis.

Former U.S. Senator Bob Kerrey is another of the 10-member 9/11 Commission who has read the 28 pages and believes they should be declassified. He filed an affidavit in support of the 9/11 families' lawsuit.

Bob Kerrey: You can't provide the money for terrorists and then say, "I don't have anything to do with what they're doing."

Steve Kroft: Do you believe that all of the leads that were developed in the 28 pages were answered in the 9/11 report? All the questions?

Bob Kerrey: No. No. In general, the 9/11 Commission did not get every single detail of the conspiracy. We didn't. We didn't have the time, we didn't have the resources. We certainly didn't pursue the entire line of inquiry in regard to Saudi Arabia.

Steve Kroft: Do you think all of these things in San Diego can be explained as coincidence?

John Lehman: I don't believe in coincidences.

John Lehman, who was secretary of the Navy in the Reagan administration, says that he and the others make up a solid majority of former 9/11 commissioners who think the 28 pages should be made public.

John Lehman: We're not a bunch of rubes that rode into Washington for this commission. I mean, we, you know, we've seen fire and we've seen rain and the politics of national security. We all have dealt for our careers in highly classified and compartmentalized in every aspect of security. We know when something shouldn't be declassified. An the, this, those 28 pages in no way fall into that category.

Lehman has no doubt that some high Saudi officials knew that assistance was being provided to al Qaeda, but he doesn't think it was ever official policy. He also doesn't think that it absolves the Saudis of responsibility.

John Lehman: It was no accident that 15 of the 19 hijackers were Saudis. They all went to Saudi schools. They learned from the time they were first able to go to school of this intolerant brand of Islam.

Lehman is talking about Wahhabism, the ultra conservative, puritanical form of Islam that is rooted here and permeates every facet of society. There is no separation of church and state. After, oil, Wahhabism is one of the kingdom's biggest exports. Saudi clerics, entrusted with Islam's holiest shrines have immense power and billions of dollars to spread the faith. Building mosques and religious schools all over the world that have become recruiting grounds for violent extremists. 9/11 Commissioner John Lehman says all of this comes across in the 28 pages.

John Lehman: This is not going to be a smoking gun that is going to cause a huge furor. But it does give a very compact illustration of the kinds of things that went on that would really help the American people to understand why, what, how, how is it that these people are springing up all over the world to go to jihad?

Tim Roemer: Look, the Saudis have even said they're for declassifying it. We should declassify it. Is it sensitive, Steve? Might it involve opening-- a bit, a can of worms, or some snakes crawling out of there? Yes. But I think we need a relationship with the Saudis where both countries are working together to fight against terrorism. And that's not always been the case.