More than four years after the September 11 terrorist attacks, the US Federal Bureau of Investigation continues to struggle to deploy the computer technologies and information-sharing capabilities critical to preventing attacks, a Senate committee heard on Tuesday.

“While the FBI has made significant progress since 9/11, its transformation into an effective domestic intelligence service is far from complete,” Charles Grassley, a Republican senator and critic of the bureau, said.

The FBI came in for the fiercest criticism of any single agency following the attacks for failing to respond to multiple warning signs that terrorists were preparing for an assault inside the US. The issue has been revived by the trial of Zacarias Moussaoui, the only one of the plotters to face a criminal trial in the US.

Jurors, who have been deliberating for more than a week on whether to sentence Mr Moussaoui to death, were told during the sentencing trial that FBI field agents had been repeatedly blocked by the bureau’s Washington headquarters in their attempts to act on suspicions about Mr Moussaoui before the attacks. One Minneapolis FBI agent told the trial that the failures of FBI management in the case amounted to “criminal negligence”.

Robert Mueller, FBI director, told the Senate judiciary committee on Tuesday that the bureau had made substantial progress in building up its anti-terrorism capabilities. It had doubled the number of intelligence analysts and deployed them in field offices across the country, and was sharing its intelligence findings across the government and to state and local police forces.

But Mr Grassley claimed that the co-operation remained largely a one-way street. “Too many federal, state and local law enforcement agencies view the FBI with disdain,” he said, because it demanded “access to the intelligence, their informants, their evidence and their resources while rarely returning the favour.”

He said the FBI continued to discourage tough oversight by punishing agents who spoke out against abuses. “For far too long, rank-and-file agents have believed that management looks out for management.”

The bureau also continues to be plagued by technology problems, though the FBI inspector-general said that improvements appeared to be on the right track. The bureau last year scrapped the so-called Trilogy project – which was launched after September 11 to give the FBI a state-of-the-art system for managing its cases. It cost more than $500m (£287m) to develop.