Evidence of a terrorist link to the Fort Hood massacre mounted yesterday with reports that US intelligence officials knew for months before the shooting that Major Nidal Malik Hasan had been trying to contact figures associated with al-Qaeda.

The gunman named in the deaths of 12 soldiers and a civilian was conscious yesterday and talking to medical staff for the first time since the attack on Thursday last week, as the FBI stepped up investigations into claims that he had maintained links with a radical cleric who once preached to two of the hijackers in the September 11, 2001 attacks.

Major Hasan had attracted the attention of US intelligence agencies several months ago with his efforts to communicate with suspected al-Qaeda leaders by “electronic means”, according to two officials briefed on classified material who spoke to ABC News.

The disclosure was seized upon by senior congressional figures angered by indications that the CIA may have withheld vital information from the army and Congress’s own intelligence and security committees. It followed a demand from Senator Joseph Lieberman for a high-level investigation into what he called “very, very strong signs that Dr Hasan had become an Islamist extremist” — signs that include apparent ties to Anwar al-Awlaki, an American-born cleric who moved to Yemen after the September 11, 2001, attacks and who called Major Hasan “a hero” yesterday.

If a link between Major Hasan and international extremists were proven, it would make the killings on the Texas army base the first terrorist attack on US soil since 2001. It would also provide a focus for critics of the Obama Administration trying to build a case that the President is less single-minded about national security than was his predecessor.

Pete Hoekstra, the top Republican on the House Intelligence Committee, said that he was furious that his committee had been denied an intelligence briefing on possible links between Major Hasan and al-Qaeda. He has written to the directors of the FBI, the CIA and the National Security Agency asking them to preserve all relevant documents for congressional review.

No sign of links to terror groups emerged from an initial inspection of Major Hasan’s computer at his flat in Killeen, Texas, according to officials, but experts have since uncovered multiple leads by combing through e-mails sent from several addresses and other computers. One of Major Hasan’s last telephone calls, made at 5am on Thursday, was to the boyfriend of a neighbour whose computer he is thought to have borrowed.

The FBI confirmed to The Times yesterday that it was assisting the army’s Criminal Investigation Command in investigations in Texas, Maryland and Virginia, where Major Hasan’s family once worshipped at the Dar al-Hijrah Islamic Centre in Falls Church.

It was unclear whether Major Hasan met Mr al-Awlaki at the Falls Church mosque in 2001 but his mother’s funeral was held there that year and a senior imam there confirmed to The Washington Post that the gunman worshipped there last year.

Mr al-Awlaki has been described as a spiritual adviser to Khalid al-Mihdhar and Nawaf al-Hazmi, two of the 9/11 hijackers who he met early in 2001 in San Diego, according to the official congressional report on the 2001 attacks. Born in New Mexico, he was investigated by the FBI but never charged with terrorist offences before his departure for Yemen, from where, as a fluent English speaker, he is believed to target potential radicals within the US through his blog.

President Obama, who has urged Americans not to jump to conclusions about Major Hasan’s motivation — even as he has been criticised for the tone and timing of his response to the massacre — will fly to Fort Hood today with the First Lady for a memorial service.

The file of apparent missed clues in this case is already thick: besides the apparent connection to Mr al-Awlaki, there is a presentation he gave to fellow combat-stress specialists in Maryland in 2007 in which he reportedly said that his faith trumped the US Constitution, and likened suicide bombers to soldiers willing to throw their bodies over those of their comrades to protect them.

“We were all very concerned about his beliefs and what he was capable of, and I’m not surprised that he did what he did,” Val Finnell, a former colleague, said. Another potential character witness who met Major Hasan when he was caring for her wounded son at the Walter Reed Army Medical Centre in Washington said simply: “I looked into his eyes, and he scared me.”

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