Intelligence officials were warned in 1995 that terrorists were plotting to hijack airliners and crash them into landmark buildings in the United States. Yet, the horrific events that unfolded on Sept. 11 took the CIA, the FBI and the rest of the U.S. intelligence community by surprise. Some experts call the attacks the worst intelligence failure in American history, while others maintain that the nation's spy agencies had no way of detecting or preventing the multipronged, international conspiracy. This much is certain: The attacks have prompted lawmakers to impose major changes on the nation's intelligence-gathering agencies. But the rush to overhaul the intelligence apparatus troubles some experts, who fear the changes will be ineffective. Others say the reforms have breached the traditional wall between criminal investigations and intelligence gathering, potentially curtailing citizens' civil liberties.

Brian Hansen, a freelance writer in Boulder, Colo., specializes in educational and environmental issues. He previously was a staff writer for The Researcher and a reporter for the Colorado Daily in Boulder and Environment News Service in Washington. His awards include the Scripps Howard Foundation award for public service reporting and the Education Writers Association award for investigative reporting. He holds a B.A. in political science and an M.A. in education from the University of Colorado.