"For one thing, granted that the higher-ups in the planning of an terrorist attack may not themselves be eager to enter the Land of Milk and Honey any time soon, your chances of capturing one of them is not that great compared to capturing one of the "field agents" (for example, someone like one of the nineteen 9/11 highjackers)" - Don Firth.

The following sort of blows that one out of the water:

"The 1993 World Trade Center bombing (February 26, 1993) a car bomb was detonated below Tower One of the World Trade Center in New York City. The 1,500-lb (680 kg) urea nitrate-hydrogen gas enhanced device[1] was intended to knock the North Tower (Tower One) into Tower Two, bringing both towers down and killing thousands of people. It failed to do so, but did kill six people and injured 1,042.

The attack was planned by a group of conspirators including Ramzi Yousef, Mahmud Abouhalima, Mohammad Salameh, Nidal Ayyad, Abdul Rahman Yasin and Ahmad Ajaj. They received financing from Khaled Shaikh Mohammed, Yousef's uncle.

In March 1994, four men were convicted of carrying out the bombing: Abouhalima, Ajaj, Ayyad and Salameh. The charges included conspiracy, explosive destruction of property and interstate transportation of explosives.

In November 1997, two more were convicted: Yousef, the mastermind behind the bombings, and Eyad Ismoil, who drove the truck carrying the bomb."

Hey Don out of those "involved" to any great degree I count seven caught.

More info:
"Agents and bomb technicians of the U.S. Treasury Department's Bureau of Alcohol, Tobacco and Firearms (ATF) responded to the scene of the blast. An ATF bomb technician subsequently found the axle in the bomb crater with the VIN of the Ryder truck that was used to contain the explosives. Further investigation by ATF found that the vehicle had been rented by a Palestinian named Mohammad Salameh. Yousef's friends reported the van was stolen in an attempt to slow investigators down.

On March 4, 1993 authorities announced the capture of Salameh. In a sweep the same day, Salameh's arrest led to the apartment of Abdul Rahman Yasin in Jersey City, New Jersey, which Yasin was sharing with his mother, in the same building as Ramzi Yousef's apartment. Yasin was taken to Federal Bureau of Investigation (FBI) headquarters in Newark, New Jersey, and was then released. The next day, he flew back to Iraq, via Amman, Jordan. Yasin was later indicted for the attack, and in 2001 he was placed on the initial list of the FBI Most Wanted Terrorists, on which he remains a fugitive today. He disappeared prior to 2003's U.S. coalition invasion in Operation Iraqi Freedom.

The capture of Salameh and Yasin led authorities to Ramzi Yousef's apartment, where they found bomb-making materials and a business card from Mohammed Jamal Khalifa. Khalifa was arrested in relation to the crime on December 14, 1994, and was deported to Jordan by the INS on May 5, 1995. He was acquitted by a Jordanian court and lived as a free man in Saudi Arabia until his death in 2007."