FBI Director Robert Mueller faced a battery of tough questions from both sides of the aisle on issues in a fast-paced Senate oversight hearing on Tuesday.
The issues ranged from why the FBI has been so slow in implementing terrorist watch lists and computer upgrades after 9/11 to questions about its investigations of US peace groups.
Often acknowledging shortcomings, Mr. Mueller insisted that the bureau was making progress.
"The FBI has changed dramatically since the events of that day, and we will continue to evolve to meet the threats," he told the Senate Judiciary Committee.
But, armed with recently released documents and oversight reports, many senators were not convinced.
"I'm very disappointed when I find that the FBI has been using new capabilities against Americans simply because they oppose the war in Iraq," said Sen. Patrick Leahy, the ranking Democrat on the panel. He cited reports of FBI surveillance of a Seattle peace festival, a Catholic peace organization in Pittsburgh, and Raging Grannies, another peace group.
Mueller said that many of these "assertions and rumors" had already been "put to bed" by an investigation by the Justice Department's Office of the Inspector General (IG), and that he welcomed another IG investigation to deal with new rumors.
The surveillance of the Thomas Merton Center in Pittsburgh, he said, was "an attempt to investigate an individual who happened to be there" - not the kind of systematic investigation of antiwar groups that set off alarms in the 1960s and '70s.
Reading from a declassified 2002 memo from a field office in Pittsburgh, Senator Leahy challenged the director to explain why the report described as its objective: "To report results of investigation of Pittsburgh antiwar activity."
In another line of questioning, senators questioned why so much surveillance of Americans had taken place out of range of a judge.
In a report to House leaders last Friday, the FBI disclosed that it had issued more than 9,200 National Security Letters (NSL) last year, covering more than 3,500 citizens or legal residents.
An NSL is a tool provided by the USA Patriot Act that allows agents to access Internet records and business files of Americans without court approval. Moreover, individuals or groups targeted by such investigative tools are under a gag order not to discuss or disclose them.
In fact, that figure does not cover the total number of NSLs - which may be much larger - because it does not include phone or Internet records, said Sen. Russ Feingold (D) of Wisconsin - an assertion that Mueller confirmed.
The FBI reports only 155 applications for access to business records using Section 215 of the USA Patriot Act - a move that does require a court order.
"It's a great disparity, and to me it points to a need for even greater protections on NSLs," said Senator Feingold, who voted against the USA Patriot Act.
Senators also challenged the director to be more responsive to congressional concerns, especially on issues relating to the expansion of executive power.
"This committee has not been able to get answers to a great many questions," said Sen. Arlen Specter (R) of Pennsylvania, who chairs the Senate Judiciary panel.
In its final report, the 9/11 commission called for an overhaul of the FBI, especially more information sharing with other agencies in the war against terrorism.
"Approaching five years after 9/11, we still do not have a domestic intelligence service that can collect effectively against the terrorist threat to the homeland or provide authoritative analysis of that threat," said John Gannon, former staff director for the House Homeland Security Committee. "I now doubt that the FBI, on its present course, can get there from here," he told the Senate panel.