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House Homeland Security Committee investigators want the 9/11 suspects questioned about the American cleric Anwar al-Awlaki and his possible role in the murder of nearly 3,000 Americans, Fox News has learned.

Three letters sent Tuesday and obtained by Fox News show the committee's investigation into the cleric, who was killed in a CIA-led operation in Yemen on Sept. 30, has broadened since his death.

In the first letter, Rep. Peter King, R-N.Y., chairman of the House Homeland Security Committee, wrote to Lt. Gen. Ronald Burgess, director of the Defense Intelligence Agency, which is responsible for directing interrogations of detainees in military custody at Guantanamo, including the self-described architect of the Sept. 11 terrorist attacks, Khalid Sheikh Mohammed.

King asked the agency to question detainees involved in plotting 9/11 about the possible roles of Eyad al-Rababah of Jordan, Daoud Chehazeh of Syria and Awlaki in the terror attack.

"I understand that these detainees have not been interrogated in several years, and certainly not since Awlaki's role within Al Qaeda became widely acknowledged in 2009," King wrote.

Al-Rababah and Chehazeh were first profiled by the Fox News Specials Unit in  "Secrets of 9/11," which aired in May. The investigation outlined the domestic support network that allowed the Sept. 11, 2001, hijackers to move around the U.S. with ease.

It also presented new and compelling evidence that Awlaki was an overlooked player in the Sept. 11 plot who slipped through the FBI's grasp after the attack.

Al-Rababah and Chehazeh, who had direct contact with al-Awlaki at his mosque in suburban Washington D.C., helped the hijackers settle in Virginia and eventually drove them to Paterson, New Jersey -- the hijackers' final stop before the attacks.

FBI Special Agent Bob Bukowski, who led the Pent-Bomb investigation team in Paterson, New Jersey told Fox News that Rababah's story did not add up in the days immediately after the attack.

Rababah "found out we were looking for him," he said. "There's no doubt when he got tipped off, he was in Connecticut at the time. He walked into the Connecticut office of the FBI and said 'oh, by the way, I just happened to meet the hijackers.' But we knew that wasn't true."

In the second letter to Secretary of State Hillary Clinton, the committee asked for help obtaining sworn testimony from al Rababah, who was deported from the U.S. to Jordan after 9/11.

Philip Zelikow, the executive director of the 9/11 Commission, told the Fox News that his investigators had wanted to question the Jordanian because they too were suspicious of his possible role in the attack, but the Justice Department denied them access.

In a third letter to Homeland Security Secretary Janet Napolitano, the committee asked that Chehazeh, also implicated in al-Awlaki's Virginia support network, not be deported "without first questioning Chehazah -- under oath -- about what role, Awlaki and their associate Eyad al-Rababah played in the 9/11 attacks."

According to investigators and declassified documents, Chehazeh told the Jordanian to go to al-Awlaki and look for work. After the meeting at al-Awlaki's Virginia mosque, Rabahah hooked up with two of the 9/11 hijackers.

In the three letters, the House Homeland Security Committee cites new evidence, including the fact that Chehazeh and Rabahah were aware of pilot Hani Hanjour's flight training. Hanjour was the pilot on United Flight 77, which slammed into the Pentagon.

And that the men were also aware of where and how Hanjour, along with fellow hijacker Nawaf al-Hazmi, bought their tickets for the attacks at a "New Jersey library compute facility," and the men's facilitation of the hijackers' movements inside the United States.

While the House Homeland Security Committee asked the FBI to provide documents and access to agents when the investigation began in May, as recently as the first week of October, Fox News was told that not a single document had been provided by the bureau.

During a hearing October 6, FBI Director Robert Mueller said he would look into the matter and a spokesman said the Justice Department and FBI "continue to work on responses to Rep King's letter and FBI officials have been in discussions with Rep. King's staff."

As part of its ongoing investigation of the cleric, the Fox News Special “The American Terrorist,” first broadcast in May 2010, showed that al-Awlaki was held in federal custody Oct. 10, 2002 at JFK International Airport because of an outstanding State Department warrant for passport fraud.

Customs documents show that an FBI agent, Wade Ammerman, ordered the cleric’s release even though the State Department warrant was still active. Al-Awlaki then appears in a high profile FBI investigation involving the same FBI agent Ammerman. The FBI has not made the agent available for questioning nor has the agency publicly explained why the cleric was allowed to slip through its grasp one year after the attacks.

Though al-Awlaki was killed nearly a month ago, King says the congressional investigation remained a priority.

“The Committee on Homeland Security is committed to determining what role these men, and any other at-large Awlaki associates, may have played in the worst mass murder in U.S. history,” he wrote in the letter.

Fox News Chief Intelligence 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 full investigate al-Awlaki’s American life, his connections to the hijackers, and how the cleric double crossed the FBI after Sept. 11.