The report, quietly released by the American National Archives over the last 18 months and described by its writers as "chilling," has drawn little public scrutiny until now.

The newly-declassified documents are hoped to help resolve the lingering mystery about what is hidden in a confidential congressional report about ties between Saudi Arabia and the 9/11 attacks.

The files detail US investigators' trip to Saudi Arabia in 2004 and their face-to-face confrontation with some of the Saudis believed to have been linked to the 9/11 hijackers on the American soil.

A key witness in the investigation has been identified as 32-year-old Fahad al-Thumairy - a former Saudi diplomat who was believed to be a ringleader of a Saudi government spy network inside the US.

Thumairy was believed to have given support to at least two of the 9/11 hijackers in California in the year before the 2001 attacks.

According to the British daily the Guardian, a former member of the investigation team has said that the newly-released files largely duplicates findings from the "25 pages" and then goes beyond it.

President Barack Obama has come under increasing pressure recently to declassify the 25 pages amid warnings that it could damage US-Saudi relations.

A memo unearthed last month noted that US investigations of the Saudi ties to terrorism had been hindered by "political, economic and other considerations."

US President Barack Obama and Saudi King Salman (R) walk together following their meeting at Erga Palace in Riyadh, April 20, 2016

Those pushing for a declassification say the report could reveal leads about the Saudis that still need to be pursued.

On Friday, a member of the 9/11 commission John Lehman said there was clear evidence that Saudi government employees were part of a support network for the 9/11 hijackers.

“There was an awful lot of participation by Saudi individuals in supporting the hijackers, and some of those people worked in the Saudi government,” he told the Guardian.

According to congressional officials, the Saudi link to the 9/11 attacks is addressed in detail in the 28 pages.

US Final Report under Scrutiny

The paperwork from the new files and the renewed debate over the 28 pages, however, is set to raise controversy because it will bring to light a final US report which was widely seen as an exoneration of Saudi Arabia.

The official 9/11 investigations have long been described as a series of whitewashes aimed at concealing the role of the Saudi government and US intelligence agencies during the period leading up to the terrorist attacks.

The newly-released files show that US investigators confronted the Saudi embassy staff in 2003 and 2004 with evidence and witness accounts confirming their links to 9/11 hijackers.

According to the report, Thumairy became angry and began to sputter when confronted with evidence of his 21 phone calls with a Saudi in the hijackers’ support network.

Two other Saudi nationals named Osama Basnan and Omar al-Bayoumi provided shelter, food and other support to two of the 9/11 hijackers – Nawaf al-Hazmi and Khalid al-Mihdhar – in the year before the attacks.

Former US senator Bob Graham, who led the joint House-Senate intelligence committee that wrote the 28 pages, has said he was convinced that Basnan and Bayoumi were low-level Saudi government intelligence officers.

Thumairy was an accredited diplomat and an imam of a large Saudi government-built mosque in southern California.

He had also been posted to the US at the request of the Saudi Ministry of Islamic Affairs, long considered by American intelligence agencies to be supportive of extremist groups outside Saudi Arabia.

FBI Concealed 80,000 Pages of Evidence  

On Friday, the US-based web publication the Daily Beast revealed that the FBI has more than 80,000 pages of documents about possible ties between the 9/11 hijackers and a high-class Saudi family.

The family reportedly lived in Florida and fled the US two weeks before the 9/11 hijackings that killed nearly 3,000 people.

According to the report, a federal judge in Tampa, Florida has been reviewing the documents for more than two years.

The review process, however, has been extremely slow because of restrictive FBI rules on how many pages Judge William Zloch may access at any one time.

The article identified the Saudi family as Abdulaziz al-Hijji and his wife Anoud, who was the daughter of Esam Ghazzawi, an adviser to a nephew of Saudi King Fahd.

Ghazzawi owned the home in which they were staying. The FBI reportedly raided the home after 9/11 but the residents had all fled in evident haste on August 30, 2001.

Visitor logs showed the alleged ringleader of the 9/11 hijackers, Mohammad Atta, had visited al-Hijji, along with two other 9/11 hijackers, Ziad Jarrah and Marwan al-Shehhi.

Former senator Robert Graham told the Daily Beast that he had never known of the FBI documents until they were uncovered by the investigative journalists.

Throughout this period, the FBI had denied that the al-Hijji family had any connection to the 9/11 attackers.

The agency reportedly changed its story only when Graham said he would testify under oath about what he had read in the file of documents. At this point the FBI conceded the existence of 35 pages of documents.

US Cover-up

The new documents add to recent revelations of evidence of Saudi ties to the 9/11 hijackers and the cover-up by the US under both the Bush and Obama administrations.

A former 9/11 commissioner who spoke to the Guardian has said the final US report underplayed or ignored evidence that Saudi officials were “part of an al-Qaeda support network that had been tasked to assist the hijackers after they arrived in the US.”

There has long been evidence that sections of the US government were aware of the plot to hijack airliners, but turned a blind eye to it.

Earlier this month, Saudi Foreign Minister Adel al-Jubeir warned the US against passing a bill that could expose Riyadh to litigation over the 9/11 attacks.

The New York Times reported last month that Riyadh had threatened to sell off up to $750 billion worth of Saudi assets in the US if the Congress passes the law, Press TV reported.

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