WASHINGTON — Anwar al-Awlaki, a radical American-born Yemeni cleric who has surfaced in multiple terror probes, is emerging as a central part of the Christmas Day airline bomber investigation, as authorities focus attention on a network of extremists in Yemen who may have helped radicalize the young Nigerian accused in the failed plot.
U.S. investigators have uncovered intelligence "chatter" indicating contacts between Mr. Awlaki, who has been under U.S. intelligence scrutiny for years, and Umar Farouk Abdulmutallab, a wealthy Nigerian who is accused of trying to down Northwest Airlines Flight 253 with explosives hidden in his underwear.
While Mr. Awlaki had been suspected of having contacts with Mr. Abdulmutallab, the evidence firms up those links.
The type and extent of the contacts detected between the two couldn’t be learned. It isn’t clear what direct role, if any, Mr. Awlaki played in the plot. Al Qaeda’s branch in Yemen, with which Mr. Awlaki is associated, has claimed responsibility for the attack.
The contacts represent another piece of the intelligence puzzle U.S. officials now say sat unconnected in different parts of the U.S.’s national-security apparatus, which the government spent billions of dollars building after the Sept. 11, 2001 attacks. President Barack Obama and lawmakers have voiced criticism of perceived intelligence lapses that allowed Mr. Abdulmutallab to get on the Northwestern flight he attempted to bomb.
Under orders from Mr. Obama, U.S. security agencies are trolling through internal reports, intercepts and other data to determine what was known beforehand about Mr. Abdulmutallab and any others involved in the attack. The president set a Thursday deadline for a preliminary report from his national-security team.
Mr. Awlaki has rocketed to prominence this year because of his role as Internet-based spiritual guide aiding the radicalization of a new generation of Islamist extremists.
Mr. Awlaki was in contact with an Army psychiatrist charged in a shooting spree last month at Fort Hood Army base in Texas.
Mr. Awlaki was among the targets in recent attacks by Yemeni security forces, with U.S. support, against al Qaeda operations in Yemen. Family members have dismissed initial reports that he was killed and his whereabouts are unknown.
Part of Mr. Awlaki’s appeal, say U.S. officials and terrorism experts, is his ability to act as a bridge between the predominantly Arab leaders of al Qaeda and willing potential jihadists in the West.
He preached at a mosque in Northern Virginia until 2002, when he left the U.S. to spend time building a following in the U.K., before returning to Yemen in 2004.
He has communicated with potential recruits through Internet Web sites and social-networking sites such as Facebook.
On his own blog, Mr. Awlaki wrote in October that Yemen was about to become a key player in global jihad. "And when this new front of Jihad starts in Yemen it might become the single most important front of Jihad in the world."
Mr. Awlaki’s following in Britain may be important to the investigation. U.S. law enforcement officials believe Mr. Abdulmutallab took his first steps toward radicalization via the Internet, most likely while in school in London. Mr. Abdulmutallab spent nearly three years at University College London, where he graduated in June 2008.
With his strong English skills, Mr. Awlaki built a substantial following in the U.K. with video and audio recordings of his sermons.
Some Muslims noticed a radical shift in his message, especially after his 2006 imprisonment in Yemen, and became increasingly uncomfortable with it.
"He blamed the whole world for his own feelings and fears," says Ajmal Masroor, spokesman for the Islamic Society of Britain.
Mr. Awlaki surfaced in the probe of the November Fort Hood shootings. Federal investigators monitoring Mr. Awlaki came across multiple communications from Maj. Nidal Malik Hasan, the man charged with the shooting spree which killed 13 people.
But they dismissed the contacts as routine and didn’t delve further. Mr. Awlaki has since claimed in interviews that he counseled Mr. Hasan.
"He’s inspirational not operational," said Bruce Hoffman, a terrorism specialist and professor at Georgetown University. "He’s not someone who commands tremendous respect for his grasp of theology or jurisprudence. He’s an effective propagandist."
Michael Rolince, a Booz Allen consultant and former FBI international terrorism chief, investigated Mr. Awlaki and his circle of associates in the U.S. following the Sept. 11, 2001, terror attacks. He uncovered contact between Mr. Awlaki and two of the 9/11 hijackers, but wasn’t able to prove it amounted to "material support" of terrorism.
"The fact he’s surfacing with such specificity in and around clear terrorists, it leaves no doubt about what business he’s been in for quite some time," Mr. Rolince said.
Mr. Awlaki, 38 years old, followed a familiar path of privileged young man to radical. Born in New Mexico to an affluent father — a former Yemeni minister of agriculture who is currently an adviser to Yemeni President Ali Abdullah Saleh — Mr. Awlaki was educated in the U.S.
After coming under the scrutiny of U.S. and U.K. authorities following 9/11, Mr. Awlaki returned to Yemen, where he continued his religious teaching and lectured at Imam University, the head of which has been designated by the U.S. and the United Nations as a terrorist financier.
In 2006, Mr. Awlaki was arrested by Yemeni authorities and U.S. investigators traveled to Yemen to interview him. He was released in December 2007, but never brought to trial.
Since his release, Mr. Awlaki left the capital and has been living mostly in his tribal region of Shabwa, according to two Yemeni journalists.
Separately, new details emerged about the two-piece device investigators say Mr. Abdulmutallab used in the botched attack.
Tests conducted on a syringe, which investigators believe was part of the device, detected traces of ethylene glycol, which is commercially available in coolants and antifreeze products, according to an FBI summary containing details of the probe reviewed by The Wall Street Journal.
The syringe is believed to have been used to detonate 76 grams of the explosive PETN, which was sewn in a pouch in the crotch of the underwear worn by the alleged bomber, the FBI document said.
—Bruce Orwall contributed to this article.