Anti-terrorism officials are increasingly concerned about American-bred extremists who travel abroad for terror training and then return home, sometimes quietly recruiting followers over the years.
Federal authorities have issued a bulletin to law enforcement agencies around the country on the heels of the arrest Monday in North Carolina of a man whose devotion to the cause of violent jihad allegedly began 20 years ago.
The internal bulletin - reviewed by The Associated Press - says the FBI and the Homeland Security Department are very worried about the danger posed by little-noticed Americans traveling abroad to learn terrorism techniques, then coming back to the United States, where they may be dormant for long periods of time while they look for followers to recruit for future attacks
On Monday, the FBI arrested Daniel Patrick Boyd, 39, charging he was the ringleader of a group of aspiring international terrorists.
The charges "underscore our ongoing concerns about individuals returning to the United States after training or fighting on behalf of extremists overseas," said Justice Department spokesman Richard Kolko.
"As a general matter, such individuals may be in a unique position to solicit others in the US to follow their example, given their combat experience, their network of overseas contacts and their credibility among young radicals seeking an authority figure," Kolko said.
Six other suspects - including Boyd's two sons - were also charged in what prosecutors say was a long-running conspiracy to train for violence and then fight overseas.
Boyd's wife, Sabrina, said in a statement Tuesday that the charges are unsubstantiated.
"We are an ordinary family," she said. "We are decent people who care about other human beings."
The internal terrorism bulletin says Boyd is part of what investigators believe is an unsettling trend of Americans attracted to terrorist groups.
Often, such individuals are what officials call "self-recruiting," using only an Internet connection to plug into a network of like-minded people who help point them toward militant groups.
Just a week ago, federal prosecutors revealed they had in custody an American, Bryant Neal Vinas, who was raised on Long Island, NY, converted to Islam and traveled to Pakistan and Afghanistan to train alongside senior al-Qaida operatives.
And on Monday, a Virginia man was sentenced to life in prison for joining al-Qaida and plotting to assassinate then-President George W. Bush. Authorities say he joined al-Qaida while attending college in Saudi Arabia.
The police bulletin, issued the evening after Boyd's arrest in North Carolina, also cites a case of what authorities say were aspiring terrorists in Oregon. In that case, prosecutors won a conviction of a man for trying to set up a terror training camp in 1999 in Bly, Ore.
Boyd and the others arrested Monday are not charged with planning attacks in the United States. Prosecutors say the seven men repeatedly traveled overseas hoping to engage in violence, and trained in military tactics at a private property in North Carolina.
The Boyds lived at an unassuming lakeside home in a rural area south of Raleigh and had a family-operated drywall business.
The indictment said Boyd, a US citizen, trained in Afghanistan and fought there between 1989 and 1992 before returning to the United States. Court documents charged that Boyd, also known as "Saifullah," encouraged others to engage in jihad.
Boyd's beliefs were so extreme that he stopped attending worship services in the Raleigh area this year and instead began holding meetings for Friday prayers in his home.
Their wives told The Associated Press in an interview at the time that the couples had US roots but the United States was a country of "kafirs" - Arabic for heathens.
Sabrina Boyd said in her statement that her husband was in Afghanistan fighting against the Soviet Union "with the full backing of the United States government."
Hilary Leila Kreiger contributed to this report