After John Walker Lindh was captured fighting alongside Taliban troops in Afghanistan shortly after 9/11, counterterrorism forces in the U.S. spent a decade worrying about a hypothetical: what if other American citizens joined forces with terrorist groups and began carrying out terrorist attacks here in the United States?
Well, as last weekend's failed Times Square car bombing clearly demonstrated, that concern is no longer hypothetical - it is becoming a reality. Just last year, 41 Americans were accused of aiding terrorist groups or plotting terrorist attacks against the U.S. or its allies.
Department of Homeland Security Secretary Janet Napolitano said earlier this year homegrown terrorism is here, and now part of the threat picture we have to confront.
The explosive-laden vehicle that was discovered in Times Square was something that New Yorkers and their police department had been expecting, they had been waiting and on the lookout for years.
New York's Police Commissioner Raymond Kelly told "60 Minutes" correspondent Steve Kroft car bombs are one of the things that worry him the most. "They're mobile. They're relatively easy to put together. You don't need much space. You can do it by yourself."
"We were lucky," Kroft remarked.
"Yes," Kelly acknowledged. "A lot of good investigative work here, but we were lucky. No question about that."
Kelly says the poorly constructed device might have killed hundreds of people if it had gone off. Instead, it took the NYPD and the Joint Terrorism Task Force just 53 hours to identify and arrest the man who built it. According to the complaint, 30-year-old Faisal Shahzad, a freshly minted U.S. citizen who had lived here for a decade, slipped off to his native Pakistan where he received explosives training, and returned to the U.S. on his on his American passport to carry out the attack.
"That is sort of a gold standard," Kelly told Kroft. "That's what al Qaeda and their surrogates look for. Someone who can travel. Someone who has clean paper. Someone who can go to Pakistan, come back and get into the United States because they're a citizen or have resident cards that get 'em back into this country. That gives them tremendous flexibility."
Asked if Shahzad was on anybody's radar, Kelly said, "No, it doesn't appear that way."
"Anything remarkable about him that would lead you to believe he might do something like this?" Kroft asked.
"No, that's a good word, unremarkable. These are unremarkable young men who make a decision to kill innocent people in their own country," Kelly said.
Asked what Shahzad has said about his motives, Kelly said, "He made a general statement that he did it because his religion was under attack."
Web Extra: Who Is Faisal Shahzad?
It is all very similar to the story of Najibullah Zazi. He was an immigrant from Afghanistan who spent much of his life in the United States, leading what seemed like a perfectly normal existence until he traveled to Pakistan in 2008 for explosives training and was later arrested in the U.S. for plotting to set off bombs in the New York City subway system.
"This is somebody that has lived here for ten years, loved playing basketball with his friends. He's a big baseball fan," attorney Art Folsom said.
Folsom was Zazi's lawyer when he began his plea negotiations with the FBI, and he says his client told them that he wanted to retaliate against the U.S. military for the innocent civilians that had been killed in his native country.
"Did you or anybody ask him if you had these feelings about the American participation in the death of innocent civilians in Afghanistan, why didn't you just speak out against it?" Kroft asked.
"He actually did bring that up. He said that if he just sat there and wrote letters to the editor, who was going to listen to him?" Folsom said. "But if he walked into a Walmart with an explosive strapped to him and blew it up, then people were going to pay attention to what it was he had to say."
But Zazi didn't reach that conclusion all by himself. He had originally gone to Pakistan to try and hook up with the Taliban to fight American troops in Afghanistan, but once there he was recruited by al Qaeda and they had bigger plans for him.
Web Extra: Al Qaeda's New Recruits
"They realized they could do more with him in the United States. And I think that they're probably very good at taking people who already have some anger or some passion about something and taking that and twisting it to go in the direction they want it to go," Folsom said.
All of this is new. For much of the past decade, the Muslim community in the United States has been well assimilated and prosperous enough to sidestep the radicalization and violence that has infected other Western countries, but now there are a few troubling exceptions.
"It all started out in Afghanistan. When we fight the oppressors straight off the land," Omar Hammami stated in a YouTube clip.
Hammami, a U.S. citizen born and bred in the American South, is now a leader of a terrorist organization affiliated with al Qaeda that's fighting in Somalia.
The recruiting video, aimed at young Muslims in America and the West, is accessible worldwide on the Internet - sometimes straight from the battlefield.
"We're planning to always put them in an ambush. Try to blow up as many of their vehicles as we can….and kill as many of them as we can….and take everything they've got. God willing," Hammami said in the video, laughing.
Hammami was raised by a Syrian father and an American mother in a middle-class home in Daphne, Ala., where he once attended a Baptist church before converting to a radical form of Islam and began, in his words, "pointing a sword" at the United States.
And there is Adam Gadahn, a Muslim convert who left his Jewish grandfather and his parent's goat farm in California a decade ago to become a spokesman and senior operative for al Qaeda. He is now a fugitive who is wanted for treason.
"I will now destroy my American passport," Gadahn said in a video.
That clip has also been all over the Internet, along with the fiery preachings of Anwar al al-Awlaki, an influential American cleric now living in Yemen, who has been linked not only to the underwear bomber, but to Army Major Nidal Hasan, who is charged with killing 13 fellow soldiers at Fort Hood, Texas.
"You can get these radical websites and these people will refer to them when they're taken into custody. And they'll talk about these websites. We monitor these websites, quite frankly. We monitor 'em with our own people who have, you know, language skills. That we've been able to use and build on," Police Commissioner Kelly told Kroft.
"What we're facing here is not an episodic series of terrorist events. What we're facing is a group of people who see themselves as revolutionaries," Phillip Mudd said.
Until he retired a few months ago, Mudd was the senior intelligence advisor to the FBI and its director. He is an authority on homegrown terrorism and believes the recent activity has been poorly organized and executed by lone wolfs or clusters of individuals who aren't part of an organized network or a terrorist cell. Instead, they see themselves as part of global movement that is being facilitated by the Internet.
"The Internet often is not the initial spark, but it helps them go down a path," he explained.
Asked what they are seeing on the web, Mudd said, "They're seeing images, for example, of children and women in places like Palestine and Iraq, they're seeing sermons of people who explain in simple, compelling, and some cases magnetic terms why it's important that they join the jihad. They're seeing images, and messages that confirm a path that they're already thinking of taking."
And according to Mudd, they are seeing all of this in English.
Those Internet messages are believed to be one of the reasons why a dental student, a tennis player pursuing a degree in business, and three friends from a mosque in Alexandria, Va. abandoned their middle class existence without telling their parents and set off for the wilds of Pakistan, leaving behind a farewell video.
They were arrested there a short time later on terrorism charges after trying to make contact with a man Pakistani authorities say is an al Qaeda commander. They are now on trial facing life in prison; their parents claim they're innocent.
"I think they went over with some clear intent in mind, and that wasn't to have a vacation," Mudd said.
According to Mudd, they left behind a video which he says he has seen.
Asked what he can say about the video, Mudd told Kroft, "They're very serious, very well thought out, very smart and very committed."
Mudd said it concerns him. "These aren't kids who read a comic book and said, 'Let me go fight the way I see fighting in a comic book.' These are kids who have seen a sophisticated magnetic ideology, and said, 'I want to sign up,'" he explained.
But by far the most troubling situation is in Minneapolis, home to more than 50,000 refugees from Somalia who were settled there after fleeing their country's ongoing civil war. Over the past two years, more than 20 young men have disappeared from their homes, and turned up fighting in Somalia, with a terrorist group called al Shabab, the same al Qaeda affiliate in which Alabama-bred Omar Hammami is a leader.
Abdirizak Bihi is a community activist in the Minneapolis neighborhood known as "Little Mogadishu," where many of the young men lived. He is also the uncle of Burhan Hassan, a high-achieving high school student who had once hoped to go to Harvard.
But on the same day that Barack Obama was elected president, he failed to return to his family apartment.
"Did you discuss with him the situation in Somalia?" Kroft asked.
"Not really. He didn't even speak Somali," Bihi said.
Asked if he went for political or religious reasons, Bihi said, "He didn't have any political, at all. His politics might lie in the championship of the NBA or the NFL."
Hassan and many of the other young men who left for Somalia spent a lot of time at the local mosque, and Bihi believes that that's where al Shabab recruiters found them and won them over with extreme religious ideology.
"He was brainwashed by the very institution we have trust him with," Bihi said.
The institution Bihi is talking about is the Abubakar As-Saddique Islamic Center.
The center is the largest Somali mosque in Minnesota. The imam, Sheik Abdirahman Sheikh Omar Ahmed, was placed on the no-fly list but his name has since been removed and he denies any involvement in recruiting any young men to fight alongside al Qaeda in Somalia.
"Well, where do you think these 20 young men got the idea to leave their parents and go off to Somalia and fight with this terrorist organization?" Kroft asked the imam
"The world is very, very small today, so open to any ideology that comes in one place in the world, you read it, immediately, on your Internet," Sheik Abdirahman replied. "You know the youth. Nobody can control their minds."
But someone helped the young men get passports, plane tickets, visas and even rides to the airport. They departed in small groups, so as not to arouse suspicion.
"This looks to me like it was pretty carefully planned," Kroft remarked.
"The level of sophistication of this process is highly underestimated," Bihi said.
One of the Minneapolis recruits, according to the FBI, has the distinction of being the first American suicide bomber: Shirwa Ahmed blew himself up while driving an explosive filled truck into a Somali government intelligence office.
Bihi says his nephew, the one who hoped to go to Harvard, is also dead, killed, he believes, by the people who recruited him for wanting to go home.
He believes Burhan Hassan was murdered by al Shabab. "Once you join, once you go over there, it's a one-way ticket.
In all, seven of the Minneapolis recruits are believed to be dead. Twelve people have been charged with aiding a terrorist group, including a former janitor at the mosque who is fighting extradition from the Netherlands.
But Stevan Weine, a professor at the University of Illinois Chicago who has spent more than a year here studying the situation, believes that a lot more than 20 young American Muslim men have gone off to fight in Somalia, their identities unknown to authorities.
And that there may be others who have been indoctrinated who are still here.
"What do you think is going [on] here? In the broader sense, that we should be worried about?" Kroft asked Weine.
"What's going on here is that young people in the refugee community are at risk for being recruited by terrorists. We have recruiters from a terrorist organization working on the ground here. We have hundreds of youth who have been radicalized. We have no policy answers to deal with those issues, as a country," he replied.
It's possible that some of the young American Muslims who have gone off to off to fight in Somalia will come back, just as Faisal Shahzad and Najibullah Zazi did when they returned from Pakistan. More dangerous than when they left.
"Every day we can't be confident we've caught every one of 'em," Phillip Mudd said. "All it takes is one or two."
"That get through the net," Kroft remarked.
"That's correct," Mudd agreed. "We can't miss."
Web Extra: Eyes In The Sky
Produced by Andy Court and Ira Rosen
for more features.