See an investigation into why authorities are concerned about the violent messages being preached outside a New York mosque on tonight's "AC 360," 10 ET on CNN.
New York (CNN) -- Outside a Manhattan mosque where the imam preaches against terrorism, the brothers of the "Revolution Muslim" are spreading a different message.
Protected by the Constitution of the country they detest, radical Muslim converts like Yousef al-Khattab and Younes Abdullah Mohammed preach that the killing of U.S. troops overseas is justified. In their thinking, so were the September 11, 2001, attacks on the United States -- and so are attacks on almost any American.
"Americans will always be a target -- and a legitimate target -- until America changes its nature in the international arena," Mohammed said in an interview to air on tonight's "AC 360."
Al-Khattab and Mohammed consider al Qaeda leader Osama bin Laden their model.
"I love him like I can't begin to tell you, because he doesn't seem to have done anything wrong from the sharia," al-Khattab said, referring to Islamic law. "If you're asking me if I love him as a Muslim, I love him more than I love myself."
They hand out fliers outside the gleaming 96th Street mosque, where up to 4,000 people visit every day. Inside the sleek, modernistic house of worship, Imam Shamsi Ali preaches against the violence that now sweeps many Muslim countries.
"What we try to do is reminding our people about the real Islam," Ali said. "We tell them what the real Islam is all about. Islam is about peace. Islam is about moderation. Islam is about friendship. Islam is opposed to any kind of hatred against anybody."
Law enforcement sources have told CNN the men walk right up to the line of protection under the First Amendment, but their message is not going unnoticed.
Al-Khattab handed CNN Correspondent Drew Griffin a business card from an FBI agent who he says is keeping tabs on him. The agent would not comment without clearance from his superiors, except to say, "Obviously, if they gave you my card, you know we are watching them."
The mosque has called police on Al-Khattab and Mohammed several times, and passers-by occasionally engage them in heated debates. Ali told CNN that ordinary Muslims are "disgusted with their behavior." But they insist they don't fight themselves, and don't incite others to do so.
Al-Khattab calls President Obama "a murderer, a tyrant, a scumbag," and says he wouldn't "shed a tear" if Obama were killed. But he added, "Would I incite his murder? That's not what I teach."
Mohammed calls himself an American "by default" who identifies with Muslims. Al-Khattab, a Jew who lived in Israel before converting to Islam, says he "would like to see a mushroom cloud" over the Jewish state -- "but before that, I'd like to see the people guided, and I'd like them to go back to their original countries where they're from."
But federal agents are not only watching them, they're watching some of those who are listening.
Neil Bryant Vinas, a young New Yorker who has pleaded guilty to plotting to attack trains on the Long Island Rail Road, met with al-Khattab. Al-Khattab said Vinas and "some brothers" traveled to Atlantic City, New Jersey, and had dinner with him. Al-Khattab said they considered him something of a hero because he left Israel and converted to Islam.
Al-Khattab also claims friendships with Tarek Mehanna, now under indictment in Boston, Massachusetts, on charges of conspiracy to provide material support to terrorists, and Daniel Maldonado, who pleaded guilty before a federal judge in Texas to receiving military training from Islamic militants in Somalia.
Mohammed says he and his fellow radicals are "commanded to terrorize the disbelievers ... making them fearful so that they will think twice before they go rape your mother or kill your brother or go onto your land and try to steal your resources."
"We are defending innocent women that are bombed every day, innocent children that are bombed every day," he said.
But asked whether those who take their fliers should take up arms against Americans, he said, "We certainly have never said that."
CNN's Paul Cruickshank contributed to this report.