Graham told the German TV program "Monitor" that 28 pages of a US government report about the attacks, which have remained classified since the first official investigation into the attacks in 2003, should be declassified.
Graham was co-chair of the bipartisan joint congressional inquiry into the intelligence failures surrounding the attacks, whose 838 page report was redacted by the Bush administration, which cited reasons of national security.
Without going into detail, the former senator says that the 28 classified pages outline a substantial network of support for terrorism in the US originating in Saudi Arabia. This is what enabled the hijackers to carry out the attacks.
"The history (of 9/11) will have to be re-written, to say that there was a support group which made 9/11 possible," Graham told the program.
"The 28 pages are primarily about the question of who financed 9/11, and the evidence points the finger at Saudi Arabia," Graham said.
The former senator was asked if the source of the funding came from individuals, the Saudi government or Saudi Arabian charities, and answered, "All of the above."
"I believe that these 28 pages will help provide additional evidence that there was systematic support, and that this support system has its primary origin in Saudi Arabia."
In April, Graham told US CBS News, "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, and 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."
The German news program contrasted the US government's refusal to reveal Saudi Arabia' role with then-US President George Bush's declaration in the aftermath of the attacks in September 2001 that he would crack down on supporters of terrorism.
This preceded a series of disastrous interventions in the Middle East, while Saudi Arabia has continued to enjoy US backing, which even extends to US logistic and intelligence support for Riyadh's own military intervention in neighboring Yemen, which has lasted since 2015.
"Any nation that continues to harbor terrorists or support terrorists will be regarded by the US as a hostile regime," said Bush, before invading Afghanistan in 2001 and Iraq in 2003, where US troops remain to this day.
