The FBI has come under attack for failing to track down terrorist suspects, including two who took part in the September 11th attacks, whose names they had been given more than two weeks before the hijackings.
Because of a lack of qualified translators, the FBI also failed to process vital intelligence and has emerged as an organisation ill-equipped to deal with the new threats of terrorism.
In the past two years, the CIA cabled to the FBI names of about 100 suspected associates of Osama bin Laden believed to be in the US or on their way. An August 23rd cable named two men, Khalid al-Midhar and Nawaq Alhazmi, who took part in the attacks, according to the Washington Post. The FBI failed to locate the men before they boarded the plane that crashed into the Pentagon.
According to the report, boxes of evidence have been piling up from previous terrorist plots, but the FBI has not had translators to decipher the documents. There is also a shortage of Arab agents.
The failures are despite an increase in counter-terrorism spending and a decision in 1998 to make terrorism a priority.
"We started down this road, but we didn't move as fast as the terrorists," said Jamie Gorelick, former deputy to the then attorney general, Janet Reno.
In a report by the National Commission on Terrorism last year, the FBI is faulted for slowness in disseminating "terrorist information that may not relate to an immediate threat". Even when it had information, the report said, the FBI sometimes did not know what to make of it. One reason, the report said, was that investigators "lack the training or time to make such assessments".
Since 1996, the FBI has been examining theories that international terrorists were using US flight schools to learn to fly jumbo jets. The FBI carried out inquiries at several schools but failed to spot any possible plot related to the US.
But in mid-August, the owners of a Minnesota flying school alerted the FBI to a man who paid cash to use flight simulators to learn how to fly passenger jets. The man, Zacarias Moussaoui, is now being hailed as a material witness but at the time was held in a local jail on immigration violations.
Ten days before the attack, French intelligence officials notified the FBI that Moussaoui was a radical Islamic extremist with possible ties to Afghan terrorist training camps, but he was not taken into federal custody.
What is coming under closest scrutiny is the bureau's inability to find al-Midhar and Alhazmi.
On August 23rd, the CIA cabled the FBI and other agencies that they should be on alert for two men with possible links to terrorists. Al-Midhar had been videotaped months before meeting a suspect in the bombing of the USS Cole, and the CIA advisory was "not a routine matter," an official familiar with the events told the Washington Post. The FBI sought the men in New York and Los Angeles but they had been living in San Diego.
One of the problems has been the shortage of Arab speakers. Last week, the FBI director Robert Mueller said there was a "critical need" for translators in Arabic, Farsi and Pashto. There has been a big response but the FBI has to ensure that no terrorist uses the post to infiltrate the organisation.
Robert Blitzer, former FBI chief of domestic counter-terrorism, estimated that the number of Arab-American agents in the organisations could be as low as 25.
"If you don't have an Arab-American agent on your staff, how the hell do you recruit Arabs?" Mr Blitzer said. "You don't even understand the culture." The FBI also faces technical problems.
More than 13,000 FBI computers are up to eight years old, meaning they cannot run current basic software.
The CIA also came under attack from politicians immediately after September 11th for failing to alert the country to the attacks.
German newspapers have reported that Mohammed Atta, who was probably piloting one of the planes that crashed into the World Trade Centre, had been under surveillance by US intelligence agents last year. Atta (33), who studied in Hamburg for eight years, is reported to have come to the attention of intelligence officers after he bought huge quantities of chemicals.
According to Focus magazine, he was suspected of buying them in order to make explosives. It said the US agents who are believed to have watched Atta between January and May 2000 did not inform the German authorities about their investigation.
Yemen has detained scores of people as it widens its investigation into possible links to Osama bin Laden, named by Washington as the prime suspect in the attacks on the United States, security officials said on Monday. Some of the arrests were based on US information.