Tamerlan Tsarnaev was the fifth man since the Sept. 11, 2001, attacks to be suspected of committing terrorism while under investigation by the FBI. http://www.nytimes.com/2013/04/22/us/boston-marathon-bombing-suspects-hoped-to-attack-again.html?ref=us Agents had questioned him a year before he traveled to Chechnya and Dagestan, predominantly Muslim republics in the North Caucasus region of Russia.  The bureau sent two counterterrorism agents from its Boston field office to interview Tamerlan and family members, a senior United States official said Saturday.
The F.B.I. responded by checking “U.S. government databases and other information to look for such things as derogatory telephone communications, possible use of online sites associated with the promotion of radical activity, associations with other persons of interest, travel history and plans, and education history,”

The FBI say they investigated, interviewed him, and found no links with terrorism. This is quite remarkable. Let me repeat it. The FBI had been warned that the man who apparently carried out the first terrorist attack on an American city since 9/11 was a strong supporter of radical Islam.http://www.bbc.co.uk/news/world-us-canada-22238705

The FBI says the Aurora teenager was arrested Friday night as he tried to board a flight from Chicago’s O’Hare International Airport to Turkey, which borders Syria. He was snared in an Internet sting after contacting a website set up by the FBI. http://www.nytimes.com/aponline/2013/04/22/us/ap-us-chicago-terror-arrest.html?ref=us