An American-born al Qaeda cleric, second only to Osama bin Laden on the world’s most-wanted list, al-Awlaki was eventually killed in Yemen last September during a US drone strike.
Despite being named a major threat by the head of Britain’s Secret Intelligence Service and the first American to become one of the CIA’s top targets, the FBI released him from custody after detaining him at JFK Airport in October 2002.
al-Awlaki, who had lived in London and thought to be behind several al Qaeda terrorist plots, had become the public face of the Islamic terrorist organisation in the wake of bin Laden’s death.
Former FBI agents said there are two possible explanations for al-Awlaki’s abrupt release in 2002. That the FBI wanted to track him for intelligence or that the bureau wanted to work with him as a contact.
Mark Giuliano, the FBI’s assistant director for national security told an enquiry yesterday that there had been conversations between an FBI agent and the US attorney in Colorado about al-Awlaki’s re-entry into the country and the warrant.
He said: ‘Yes, sir, there was a dialogue, as there always will be.
‘If a case agent has a case on somebody that is coming into the country, the system is triggered and set up so that there will be a call to that case agent.’
But Mr Giulano could not explain how the FBI knew of the terrorist’s return to America nor the reasons why he was allowed to walk free from custody.
At a hearing yesterday into the Webster report into the bureau’s intelligence failures leading up to the Fort Hood massacre, in which Major Nidal Hasan was accused of killing 13 people and wounding 32 in Texas, links were made between Hasan and Al-Awlaki.
In an exchange of 19 emails Hasan told al-Awlaki that he advocated using suicide bombers and that he believed it was OK to kill civilians to which al-Awlaki replied that Hasan should keep his contact details handy.
Republican Rep Frank Wolf, chairman of the committee that oversees the FBI said at a hearing: ‘I really want to get to the bottom (of this)’ according to Fox News.
‘We’re going to send a letter on this. If we can, we’re going to get a hearing, and if we have to, we may even subpoena the thing.
al-Awlaki was being held when FBI agent Wade Ammerman told customs agents that ‘the warrant…had been pulled back’ but documents show that the warrant was still active at that time and was only relinquished later that day.
The bureau has always maintained that the case against al-Awlaki was weak and the pulling back of his arrest warrant was coincidental with the day he returned to America.
Why he was able to walk free when scores of Muslim men were held in detention centres on material witness warrants in the wake of September 11 attacks has never been explained by the FBI.
The terrorist has also been linked to September 11 hijackers, and was widely believed to be the mastermind behind a number of terror atrocities, the leader of Al Qaeda in the Arabian Peninsula and inspired attacks by Muslims inside the United States including the Fort Hood massacre.
Mr Giuliano said: ‘If a prosecutor at that time, regardless of whether a call was made or not, looks at the evidence and decided there was not enough to be able to arrest that individual, the warrant would be dropped.
‘I assure you … if we could have incarcerated al-Awlaki, we would have.’
But past and present investigators have said that once a warrant is signed off by a federal judge, it is not routine to review it.
They have also questioned why an exemption was made for a person who under an FBI investigation because of his links to September 11 hijackers.
Mr Giuliano said the FBI will make a decision within 60 to 90 days, based on the findings of the report by former FBI and CIA director William Webster.