The threat of "homegrown" terrorism — highlighted this week by news of a plot to attack Fort Dix — could surface again in the future, a high-ranking FBI official told members of a Senate panel.
Officials from the bureau and a number of other government agencies discussed the issue in an appearance Thursday before the Senate's Homeland Security Committee.
The hearing came just days after six foreign-born men living in New Jersey were arrested for an alleged plot to attack Fort Dix.
Sen. Joseph Lieberman of Connecticut, the committee chairman, asked the FBI's assistant director, John Miller, how a handful of immigrant men who outwardly seemed to be fitting into American society could decide to attack it.
"We saw in this case, these immigrants — three here legally and three not — who seemed to be making their way in America, yet got radicalized and allegedly were planning this," Lieberman said. "From the FBI's large interaction with the Muslim community, should we expect more homegrown terrorist attacks?"
Miller said yes. These kinds of arrests and these kinds of cases in which longtime residents of the United States unilaterally declare jihad are likely the wave of the future.
"You see a certain tempo of activity of U.S.-based, self-initiating, self-radicalizing, self-financed groups coming together," Miller said.
But he noted that in "the context of the larger Muslim population," those groups represent only "a few" individuals.
Still, the FBI is asking tough questions about those "few," Miller said, including: "Where did they become radicalized? How did they become radicalized?"
Miller said the FBI and a number of other government agencies were still searching for clues.
"We are looking hard at this," he said. "We are working closely with the Department of Homeland Security and the larger intelligence community and the DNI to try and figure out if there are a set of models or anything that will tell us better where to lay those trip wires to look for people who are going over the line from radical ideas, which is legal in a free society and encouraged, to going operational and finding where to set those trip wires has been a daunting and amorphous task."
Lieberman seemed sympathetic.
"In the ideal world, you'd be able to follow the profile to prevent the radicalizaton of these individuals," he noted.
Miller said they were trying. Law enforcement officials told NPR that was going to be the concentration of the FBI's efforts on the edges of the Fort Dix case in the coming weeks. They want to understand who radicalized the men and when it happened.
To better understand these kinds of questions, the FBI has started to engage Muslim organizations such as the Islamic Society of North America and the Muslim Public Affairs Council. At the hearing, Miller said the bureau has started to make conference calls to the group when there is an incident or arrests like the ones in New Jersey.
"This kind of spontaneous dialogue has become part of our set operating plan when there is a breaking event on terrorism as we know that it can bring stress on Arab-American and Muslim communities," Miller said.
Of course, the outreach isn't entirely altruistic. Investigators are keenly aware that their best chance at stopping an attack before it begins is through ordinary citizens — someone who sees something and reports it.
As the investigation into the case continues, NPR has learned that agents found what they believe to be the six guns the men used during shooting sessions in the Pocono Mountains.
Officials also found a spotter's scope, something snipers use to target their shots.