The Chicago terrorist David Headley is on the list of five who were known to the FBI and then went on to actually commit a terror attack. Headley, now in the company of one of the Boston Marathon bombers, and several other notorious terrorists--prompting questions about who knew what, when and why weren't they stopped.
After the marathon bombing was traced to Tamerlan Tsarnaev, so was the fact that he had been questioned by the FBI in 2011 at the request of Russian counter-terrorism officials.
But American investigators determined Tsarnaev had no ties to terror after reviewing his Web habits, phone records and associates.
"As far as getting information in advance and not seeming to take the proper action, this is at least the fifth case that I'm aware of that the FBI has failed to stop someone who ultimately became a terrorist murderer," said Rep. Peter King (R-NY), who sits on the House Intelligence Committee.
- The Tsarnaev failure was preceded by Anwar al-Awlaki, a U.S.-born citizen of Yemeni heritage who directed numerous terror attacks. He was known to the FBI since 1999 and even questioned after 9/11.
- Nidal Hassan, the U.S. Army major charged in the worst-ever shooting on an American military base. Thirteen dead, 30 wounded. His relationship with Awlaki was known to the FBI but nothing was done.
- Abdulhakim Muhammed. While under investigation by the FBI for terror links, he murdered two Army privates in Arkansas.
- And David Coleman Headley. The Pakistani-Chicagoan was an operative for an al-Qaeda offshoot and scouted targets for the 2008 Mumbai massacre, an attack that left 160 dead came after Headley was a U.S. drug informant and had been questioned by American defense investigators.
"Police did a magnificent job bringing this nightmare to an end in less than a week," said Rep. Michael McCaul (R-TX), who is Homeland Security Committee chairman. "So, I commend what they did. My job as chair of Homeland Security is to review these matters, what if anything went wrong and how can we prevent that in the future."
While there are five cases of known or suspected terrorists falling through the cracks of law enforcement, federal authorities point out that they have fielded thousands upon thousands of tips and potential evidence since 9/11, that the vast majority of potential suspects have been dealt with, and that many terrorist plots have been stopped.