WASHINGTON — In nearly a dozen recent terrorism cases in the United States, Britain and Canada, investigators discovered the suspects had something in common: a devotion to the message of Anwar al-Awlaki, an eloquent Muslim cleric who has turned the Web into a tool for extremist indoctrination.
Mr. Awlaki, 38, the son of a former agriculture minister and university president in Yemen, has never been accused of planting explosives himself. But experts on terrorism believe his persuasive endorsement of violence as a religious duty, in colloquial, American-accented English, has helped push a series of Western Muslims into terrorism.
Maj. Nidal Malik Hasan, the Army psychiatrist charged with killing 13 people at Fort Hood, Tex., on Nov. 5, is only the latest suspect accused of perpetrating or plotting violence to be linked to the cleric.
Evan Kohlmann, a counterterrorism researcher who has testified in terrorism trials in the United States and United Kingdom, said Mr. Awlaki’s work had also turned up in cases in Chicago and Atlanta and in at least seven in the United Kingdom.
“Al-Awlaki condenses the Al Qaeda philosophy into digestible, well-written treatises,” Mr. Kohlmann said. “They may not tell people how to build a bomb or shoot a gun. But he tells them who to kill, and why, and stresses the urgency of the mission.”
For at least a decade, counterterrorism officials have had a wary eye on Mr. Awlaki, an American citizen now living in Yemen. His contacts with three of the Sept. 11 hijackers, at mosques where he served in San Diego and Falls Church, Va., remain a perplexing mystery about the 2001 attacks, said Philip Zelikow, who was executive director of the national 9/11 commission.
But in recent years, concerns have focused on Mr. Awlaki’s influence via his Web site, his Facebook page and many booklets and CDs carrying his message, including a text called “44 Ways to Support Jihad.”