The U.S. Justice Department said Adam Gadahn, 28, is the first U.S. citizen charged with treason since the World War II era. A conviction on treason carries penalties up to the death penalty.
Gadahn, a former Orange County, Calif., resident, is also known as Azzam al-Amriki or Azzam the American. Of Jewish-American ancestry, he converted to Islam as a teenager. He has been out of the country since 1998.
He appeared in several videotapes broadcast between October 2004 and Sept. 11 of this year, the department said. In the first tape, Gadahn said he had joined al-Qaida, and that "the streets of America shall run red with blood."
Al-Qaida has taken responsibility for the Sept. 11, 2001, terror attacks on the World Trade Center in New York and the Pentagon near Washington.
In September 2005, Gadahn called the attacks "the blessed raids," referred to other attacks and said, "Tomorrow, Los Angeles and Melbourne, Allah willing."
The indictment was handed down in Santa Ana, Calif.
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