But his devotion eventually spiraled into trouble — and an arrest.
Gadahn, who was, was later expelled from the mosque after attacking an employee. Records show he pleaded guilty to assault and battery charges in June 1997 and was sentenced to two days in jail and 40 hours of community service.
"He was becoming very extreme in his ideas and views," said Muzammil Siddiqi, the society's religious director. "He must have disliked something."
The other six alleged al Qaeda operatives whose photos and backgrounds were highlighted Wednesday have been the subject of FBI pursuit for months. Gadahn is the only U.S. native among the seven and the only one whose name was first publicly disclosed Wednesday.
Gadahn's alleged journey from student of Islam to suspected terrorist startled his brother, Omar Gadahn, 17, who first heard the FBI's announcement on the news.
"I don't believe it, but I don't know. Anything is possible," he said at the family home in Santa Ana. His brother "wanted to follow what he believed and that's what he did."
Asked about allegations that his brother might be conspiring to act against the United States, the teen said he'd never heard his brother say anything against the country.
His father Phillip Gadahn says Adam Gadahn always was a seeker and on a Web site under his name he wrote he'd found what he was searching for in Islam, reports CBS News Correspondent Bill Whitaker.
"I discovered that the beliefs and practices of this religion fit my personal theology and intellect," he wrote. "Having been around Muslims in my formative years, I knew well that they were not bloodthirsty, barbaric terrorists."
According to the FBI, Gadahn, 25, attended al Qaeda training camps and served as an al Qaeda translator. The agency said he is being sought for "possible terrorist threats against the United States." He also goes by the names Adam Pearlman and Abu Suhayb Al-Amriki.
Omar Gadahn, a college student, said he hasn't seen his brother in about five years. His mother last spoke to him by phone in March 2001. At that time he was in Pakistan, working at a newspaper, and his wife was about to have a child.
The man's father, Phillip Gadahn, said he didn't think his son had been a part of a terrorist organization. He told a local television station that FBI agents told him his son was not wanted and no arrest warrant had been issued for his son's arrest.
"I knew he'd been out of the country, and I thought he was settling down," he said. "I didn't imagine he was involved in anything. ... I'm not sure the FBI really thinks that."
FBI officials in Los Angeles said Adam Gadahn was last known to be in Southern California in 1997 or 1998.
Terror experts say Gadahn, like American Taliban John Walker Lindh, is just what al Qaeda is seeking: a malleable American convert, a true believer who can blend in, reports Whitaker.
Gadahn was home-schooled at the family farm in Riverside County. He did not attend college. Omar said the family was a "more or less Christian household, but no one was particularly religious."
Omar said he doesn't know why his brother converted to Islam. But a statement attributed to Adam Gadahn on several Muslim-related Web sites said he "gradually realized I could not be a Christian."
Gadahn's aunt Nancy Pearlman described her nephew as inquisitive and quick to learn languages. He read about several religions, she said, noting his mother's family is Roman Catholic and his paternal grandfather Jewish.
"He was raised to be religious, to believe in a God," Pearlman said outside her Los Angeles home. "He made his own choice. We all make our own choices in life."
"There was no indication he was involved with terrorists at all," Pearlman added. "He was never fanatical. I never saw it in him."
The other six suspects discussed by federal authorities on Wednesday were Adnan G. El Shukrijumah, a Saudi native who used to live in South Florida; Aafia Siddiqui, a Pakistani woman who studied at the Massachusetts Institute of Technology; Fazul Abdullah Mohammed, a native of the Comoros Republic; Ahmed Khalfan Ghailani, a Tanzanian who is under indictment for the 1998 embassy attacks; Amer El-Maati, born in Kuwait and wanted by the FBI for questioning; and Abderraouf Jdey, a Tunisian who was among five men who left suicide messages on videotapes recovered in Afghanistan.