When he was arrested Friday in Washington, he was carrying with him a vest supposedly packed with explosives, but the material inside was not actually dangerous, Fox News was told.
A short time earlier, he had been praying at a mosque in the Washington area. His destination was Capitol Hill.
The public was never in danger, as he had been under constant surveillance for some time, officials said.
In a statement that did not get into the details of the alleged plot, the U.S. Capitol Police said the suspect was "closely and carefully monitored." Capitol Police confirmed the suspect was arrested on Friday.
"At no time was the public or congressional community in any danger," the department said.
A senior source involved with law enforcement at the Capitol also told Fox News the investigation was "all very controlled." The source said the U.S. Capitol Police was involved with the FBI and other agencies in tracking the suspect "not more than a year."
An arrest usually indicates charges have been filed in some form, but it's unclear when or how charges would have been filed in this case. It's also unclear if the suspect will be appearing in court Friday. In similar past cases, suspects have made their initial court appearance within hours of their arrest.
Sites in Washington have long been a target for terrorists, especially self-radicalized extremists caught in FBI stings.
In September, a Massachusetts man was arrested for allegedly plotting to fly bomb-laden model planes into the Pentagon and U.S. Capitol. FBI agents claiming to be associates of Al Qaeda provided 26-year-old Rezwan Ferdaus with what he thought was explosive material for the remote-controlled planes.
Nearly a year earlier, a Virginia man was arrested for trying to help Al Qaeda plan multiple bombings against Washington's Metrorail system. For months, 34-year-old Farooque Ahmed of Ashburn, Va., had been meeting and discussing "jihad" with individuals he thought were affiliated with Al Qaeda, but in fact he was meeting with FBI agents.
In the past year alone, at least 20 people have been arrested in the United States on terrorism-related charges, according to the Senate Select Committee on Intelligence.
"Most of the arrests" have involved "lone wolves," radicalized online and able to use the Internet to build bombs, FBI Director Robert Mueller told the Senate committee last month.
At the time of Ahmed's arrest in October 2010, the U.S. Attorney for the Eastern District of Virginia, Neil MacBride, said the case showcases "our ability to find those seeking to harm U.S. citizens and neutralize them before they can act."
Fox News' Chad Pergram contributed to this report.
Read more: http://www.foxnews.com/politics/2012/02/17/feds-arrest-man-heading-to-us-capitol-for-suicide-mission/print#ixzz1mfOQ9Z32