While Dr Rice focused on a broader picture, saying there was 'no silver bullet' that could have prevented the September 11, 2001 attacks, Mr Ashcroft quickly went on the offensive. He explained in his opening statement that he had argued for changing the rules for FBI covert operations to allow for the assassination of persons deemed a threat to the country rather than only their capture.

'My formal review found no covert action programme to kill [Osama] bin Laden, only a covert action programme to capture bin Laden,' he said. 'Our agents were given only the language of lawyers.'

Mr Ashcroft also answered questions about the Patriot Act, a reform of Justice Department policies passed after the terror attacks that has been criticised as a platform for taking away civil liberties.

There are 768 detainees, mostly picked up on visa violations, being held in the US without formal charges that previous to the Patriot Act would have been inadequate to keep them jailed.

Mr Tenet testified that when he took over the agency in 1997, it was an operation in decline.

'The nation's human intelligence capability was in disarray,' Mr Tenet said during his opening statement, noting that it would take at least five years for the CIA to function as needed. 'We had to overhaul our recruitment and training strategy to build up our human intelligence.'

Mr Tenet stopped short of a direct apology to the families of those killed, but did admit to failure.

'All of us took little action to create a common arena of criminal and intelligence data arena we could access,' Mr Tenet said.

'The bottom line is, to do this right, to build the platforms and access and cover and technology that we need, it's budgeted for.'