A former Guantanamo Bay detainee with Al Qaeda ties was in Benghazi the night of the Sept. 11 attack, according to a source on the ground in Libya.

The source told Fox News that ex-detainee Sufian bin Qumu, who is suspected of running camps in eastern Libya where some of the assailants trained, is also a "respected member" of Ansar al-Sharia -- one of the Islamist groups identified in State Department email traffic two hours after the attack.

Two sources familiar with the investigation, when asked about bin Qumu's whereabouts the night of the attack, did not dispute the claim he was in Benghazi.

While it is not clear whether bin Qumu was directing the assault, his security file from Guantanamo may be revealing. Having already trained in Usama bin Laden's camps, in 1998 bin Qumu joined the Taliban in Pakistan and "communicated with likely extremist elements via radio during this period indicating a position of leadership," the file shows.

Fox News' ongoing reporting on the attack has shown that at least four key Benghazi suspects have ties to the Al Qaeda senior leadership in Pakistan. They include bin Qumu and Muhammad Jamal, whose network is also suspected of training jihadists for the attack. Jamal was held, and later released by, Egyptian authorities. Earlier this month, the State Department's terrorist designation for Jamal and his network cites letters he exchanged with Al Qaeda leader Ayman al-Zawahiri, where Jamal asked for money and explained the scope of his training camps, which included Libya and the Sinai.

Fox News was first to report that two other suspects have ties to the Al Qaeda senior leadership -- one believed to be a former courier and the other, a bodyguard for the network. Faraj al Chalabi, identified to Fox News as the bodyguard, was also in Afghanistan with bin Laden until the U.S. invasion in October 2001.

The hunt is still underway for suspects in the attack more than a year later, though some have questioned the administration's resolve.

After Fox News reported earlier this week that the Benghazi suspects are not included on the State Department's "Rewards for Justice" program, which offers cash for tips that lead to suspected terrorists, Republican Rep. Michael McCaul, chairman of the House Homeland Security Committee, wrote to Secretary of State John Kerry questioning the omission.

The letter is now being circulated on Capitol Hill for signatures, Fox News has learned, and should be delivered to Kerry's office no later than next week.

A draft reviewed by Fox News includes highly critical language. "We fail to understand how such an important counterterrorism tool could not be used by the administration, when you and the president claim that bringing the assailants to justice is such a high priority," the draft says.

Bin Qumu was transferred to Guantanamo on May 5, 2002, and released to Libya on Sept. 28, 2007, where he was initially held and later released. His Guantanamo review file, originally a classified document but made public by WikiLeaks, says he is a "former member of the Libyan Islamic Fighting Group (LIFG), a probable member of al Qaida and a member of the North African Extremist Network. Detainee is a medium to high risk and he is likely to pose a threat to the US and it's interests and allies."

A review of State Department cables, also made public by WikiLeaks, shows that former Ambassador Chris Stevens, who was killed in the 2012 attack, was interested in bin Qumu's fate once he was transferred from the U.S. military detention facility to Libya. Stevens had one of his subordinates meet with bin Qumu at the Libyan jail.

Before he was promoted to U.S. ambassador to Libya in May 2012, Stevens served as CDA, or "Charge de Affairs," at the embassy in Tripoli. In 2008 cables, Stevens noted that he and his team from the politics and economic section of the embassy were visiting prisons to ensure the welfare of repatriated Guantanamo detainees from Libya. This included bin Qumu, who is referred to as ISN 557 in the cables dated from September 2008.

One cable says: "During our previous meeting on June 10, the security official who facilitated the meeting explained that detention protocols for extremists and terrorists mandate that they be held in solitary detention to preclude the possibility that they could recruit other members of the prison population. End note."

Former U.N. Ambassador John Bolton noted to Fox News that "as we returned Gitmo inmates to Libya to be imprisoned by Muammar Qaddafi, the U.S. government was tasked with officially inquiring about their welfare in Libyan prisons."

Fox News' Bret Baier was first to report last fall that the intelligence community believed the former detainee was involved in the Benghazi terrorist attack.

Representatives with the CIA and National Counterterrorism Center declined to comment for this report. The FBI did not respond.