A secret 9/11 history exists - one that the few who know it say names at least one foreign country that provided support to some of the 19 hijackers on their murderous mission 13-years ago on Thursday.

Twenty-eight pages from an official 2002 report detailing foreign-government assistance to the September 11 attackers remain classified. Determined 9/11 family members and sympathetic congressmen are pushing hard , however, for the long-awaited release of the missing history of one of the United States' greatest tragedies.

The controversial information is contained in the House-Senate Intelligence Committees' Joint Inquiry . The section on "specific sources of foreign support" was classified by former president George W Bush for national security reasons.

Bush received his share of flak for the move, but critics have also denounced President Barack Obama, who reportedly told several 9/11 family members he would declassify the 28 pages - but years later has still failed to do so.

Observers say the American public - and 9/11 family members in particular - deserve to know what the missing chapter reveals.

'Heinous plot' It was the worst-ever attack on American soil on September 11, 2001, when four hijacked airliners crashed into the World Trade Center's Twin Towers, the Pentagon, and a field in Pennsylvania on a sunny Tuesday morning.

Terry Strada's husband Tom died in the World Trade Center's North Tower. She's now the co-chair of the group 9/11 Families United for Justice Against Terrorism, which represents more than 9,000 people. Thirteen-years later, she told Al Jazeera, no justice has been served for the atrocity that killed nearly 3,000 people.

"The victims' families and survivors want to hold those accountable for the murder, pain and suffering that was inflicted on us," Strada said.

"My husband was killed by radical Islamist terrorists on American soil who cannot operate without massive amounts of money and support. The hijackers are dead. I want to know who gave them the funds and/or material support needed to carry out their heinous plot and hold them accountable. Then justice will be served."

The push to declassify the chapter on foreign support is not a new one, with 46 US senators seeking the 28-page publication in 2003. Obviously, that move failed.

US Congressmen Walter Jones, Stephen Lynch, and Thomas Massie - who have read the 28 pages - sponsored Resolution 428 last December, seeking the immediate release of the classified 9/11 history. Joining with family members, the politicians reiterated their call for declassification at a Tuesday press conference in Washington, DC.

"I think the 28 pages are stunning in their clarity in terms of how demonstrative they are in showing the planning beforehand, the financing, and the eventual attacks on that day," said Lynch, adding questions remain whether individuals identified "were acting as part of a government, or acting as rogue agents".

Understanding history

The 28 pages can be read by members of Congress who ask permission from leaders of the House and Senate Intelligence Committees. Once authorised, the politicians are led by intelligence officers to a special sound-proof room to read the redacted chapter. An officer remains present the entire time, ensuring that no notes are taken. No specific details from the 28 pages can be divulged to the public.

Pictures of some of the hijackers at the National September 11 Memorial Museum in New York City [Getty Images]

Congressman Massie has described the classified chapter as "shocking".

"I had to stop every couple pages and just sort of absorb, and try to rearrange my understanding of history for the past 13 years, and years leading up to that," he told a press conference earlier this year.

"It challenges you to rethink everything."

Steven Aftergood monitors government secrecy for the Federation of American Scientists . He told Al Jazeera while the information might negatively affect US foreign relations, the importance of shedding light on the September 11 attacks takes precedence.

"In other cases, that might be enough to warrant classification. But in this case, the need to clarify the background of the 9/11 attacks is an overriding factor and it should compel disclosure, in my opinion. Sooner or later, that will happen. Sooner would be better," said Aftergood.

Edward Price, assistant press secretary at the National Security Council, said the Office of the Director of National Intelligence (ODNI) was looking at the issue. "Earlier this summer the White House requested that ODNI review the 28 pages from the joint inquiry for declassification. ODNI is currently coordinating the required interagency review and it is ongoing."

Accusations

Former senator Bob Graham co-chaired the 2002 House-Senate Joint Inquiry, the first official investigation into 9/11, and oversaw the writing of the 28 pages. Al Jazeera requested an interview with Graham but received no response.

For years Graham has prodded the White House to release the information. He has also gone on record accusing Saudi Arabia of ties to the September 11 attacks.

Saudi Arabia has nothing to hide. We can deal with questions in public, but we cannot respond to blank pages. - Prince Bandar bin Sultan, former Saudi ambassador to the US

Nawaf al- Hazmi and Khalid al- Mihdhar were the first two 9/11 hijackers to enter the United States in January 2000. They were soon befriended by Saudi national Omar al-Bayoumi , who helped them find an apartment in San Diego, co-signed their lease, and paid their security deposit.

Graham accused Bayoumi of being a "Saudi government agent" who "provided direct assistance" to the two hijackers.

Michael Kellogg is a Washington, DC-based lawyer for the Saudi Arabian government. He told Al Jazeera the allegations against Bayoumi were "carefully examined and rejected" by the 9/11 Commission Report in 2004.

"Mr Bayoumi was attending school in London at the time of the attacks, and there is no known basis for the allegation that he was an intelligence agent, or in any way involved in those attacks," Kellogg said.

Prince Bandar bin Sultan was the Saudi ambassador to the United States on September 11, 2001. He denied any Saudi role in 9/11 in a 2003 statement .

"The idea that the Saudi government funded, organised or even knew about September 11 is malicious and blatantly false," said Bandar.

Saudi Arabia, interestingly, has also called for the declassification of the secret 28 pages on foreign support.

United Airlines flight 175 flies into World Trade Center's South Tower on September 11, 2001 [Getty Images]

"In a 900-page report, 28 blanked-out pages are being used by some to malign our country and our people," Bandar said in 2003.

"Saudi Arabia has nothing to hide. We can deal with questions in public, but we cannot respond to blank pages."

Solving the mystery

So what foreign government or governments supported the hijackers? Only by releasing the 28 pages can anyone know for sure, declassification proponents say.

For Terry Strada, who marks 13 years without her husband on Thursday, understanding the full history of the 9/11 plot is essential for the United States - and for herself.

"It's important to know the truth regarding who was giving support to the hijackers in order to know who we can and cannot trust going forward," said Strada.

"And personally, it's important to me to know who was behind the murder of my husband and many dear friends."