Declassified documents, exclusive interviews and phone and banking records present an overwhelming case that the 9/11 hijackers relied heavily on a domestic support network to facilitate the plot.
Former Sen. Bob Graham, D-Fla., who led the first congressional investigation into the 9/11 attacks in 2002, was asked by the Fox News Specials Unit if he believes the hijackers' support network remains in place today because it was never fully identified or disrupted after the attacks.
"I have no reason to believe it's not," Graham told Fox News.
The findings of an 18-month investigation by Fox's Specials Unit, called the "Secrets of 9/11," to be broadcast Saturday at 10 p.m. ET, shows that some members of the suspected Al Qaeda support network entered the U.S. nearly a decade before the attacks and that others are still living here in plain sight.
The House Homeland Security Committee shares these suspicions. A letter, first obtained by Fox News, states that the committee, chaired by Rep. Peter King, R-N.Y., has launched a congressional investigation into the New Mexico-born cleric Anwar al-Awlaki and his likely role as a 9/11 facilitator.
Writing to Attorney General Eric Holder in May, King explained the committee's objectives.
"The Committee on Homeland Security has initiated an investigation into Al Qaeda in the Arabian Peninsula terrorist Anwar al-Awlaki's possible involvement in the planning and execution of the September 11, 2001 terrorist attacks on the United States, including assisting, facilitating and mentoring 9/11 hijackers Khalid al-Mihdhar, Nawaf al-Hazmi and Hani Hanjour," he wrote.
Declassified documents also show al-Awlaki was investigated by the FBI at least two years before the attacks because of his association with a suspicious Yemeni charity.
"Secrets of 9/11" exposes the connections between al-Awlaki, his San Diego mosque and the hijackers al-Mihdhar and al-Hazmi. They were the first two hijackers into the U.S. in January 2000 -- arriving at least six months ahead of Mohammed Atta. They were the beachhead for the operation.
One question was never answered: Why would Khalid Sheikh Mohammed -- the self-described architect of 9/11 -- send two of his most experienced hijackers, who spoke virtually no English, to the ghetto of Southern California unless there was someone there to meet them?
The executive director of the 9/11 Commission, Philip Zelikow, told Fox News his team was deeply suspicious of al-Awlaki and his contacts with the hijackers in San Diego and in Falls Church, Va.
"We put the spotlight on Awlaki about as brightly as we could and as brightly as a government agency could," Zelikow explained.
Graham said he was always troubled by the hijackers' so-called chance meeting with a Saudi called Omar al-Bayoumi who was connected to al-Awlaki. Bayoumi claimed to meet al-Hazmi and al-Mihdhar by accident at a Los Angeles Middle Eastern restaurant in January 2000.
"There were 134 Middle Eastern restaurants in Los Angeles in January 2000. We had a statistician do a probability that four people would end up at the same place at the same time and it was more than five million to one," Graham told Fox News.
Graham believes the "chance" meeting between the hijackers and the Saudi was planned.
"My assumption is that the one-hour meeting with Bayoumi, he was directed to go to this restaurant and that the two hijackers had similarly been directed to go to the restaurant so that they would have this opportunity to meet and discuss the possibility of relocating to San Diego," Graham said.
Eleanor Hill, the chief of staff for the Joint Congressional Inquiry, said the FBI was concerned about Bayoumi, who claimed to be a 44-year-old student in the U.S., long before the Sept. 11 attacks.
"Bayoumi -- he was one of the individuals who had been the subject of a counterterrorism investigation or inquiry by the FBI and, lo and behold, ends up being really very helpful to two of the hijackers in California. He basically invites them to San Diego, he takes them around in San Diego, he helps them get an apartment, he puts down the deposit for their first apartment," Hill said.
Graham told Fox News there was no evidence, as stated in the 9/11 Commission report, that the hijackers ever paid the Saudi back for the rent deposit on their San Diego apartment. It was not far from al-Awlaki's mosque where the hijackers met with him -- inside a small upper floor anteroom -- on a regular basis.
"Our investigation did not find any record to support the argument that they (the hijackers) had reimbursed Bayoumi. Our conclusion was that this was one of the services that Bayoumi had been directed to provide," Graham said.
Graham said the hijackers were also big spenders in San Diego. "The lifestyle of al-Hazmi and al-Mihdhar became very expensive. Among other things, they like to go to bars. And they spent a lot of money, in fact, al-Hazmi at one point wanted to marry strippers that they had met at the bar."
Hill added that there is little doubt al-Awlaki, using his mosque as a base, along with his associates, facilitated the hijackers in San Diego in 2000. A year later, the same pattern was repeated in Fall Church at al-Awlaki's new mosque.
"There was a lot of smoke. ... There was a lot of connection between al-Awlaki and the two hijackers in California. And then al-Awlaki moved to a different mosque, and lo and behold, shortly after that the hijackers go to Fall Church and go to Virginia," Hill explained. "They go to the mosque that al-Awlaki is at, just as in California, you have an associate of al-Awlaki ... taking them around and helping them get settled."
For the first time, "Secrets of 9/11" documents how phone records link the fax number for al-Awlaki's Virginia mosque to one of the 9/11 conspirators on trial at Guantanamo Bay. Bank records also show hijacker Hani Hanjour forwarded his utility deposit from Arizona to the same Falls Church mosque after his pilot training concluded in March 2001.
The 9/11 commission's Zelikow told Fox News that he believed Khalid Sheikh Mohammed never came clean on potential U.S. contacts for the plot.
"KSM was asked, many times, about whether there were contacts in the United States. And ... he always seemed to blow smoke in answering questions like this," Zelikow said.
National Correspondent Catherine Herridge's bestselling book "The Next Wave: On the Hunt for al Qaeda's American Recruits" was published by Crown on June 21st. It draws on her reporting for Fox News into al-Awlaki and his new generation of recruits -- al Qaeda 2.0. It is the first book to fully investigate al-Awlaki's American life, his connections to the hijackers, and how the cleric double crossed the FBI after 9/11.
Catherine Herridge is an award-winning Chief Intelligence correspondent for FOX News Channel (FNC) based in Washington, D.C. She covers intelligence, the Justice Department and the Department of Homeland Security. Herridge joined FNC in 1996 as a London-based correspondent.