FBI fouls up 11 September email investigation

The FBI's investigation of suspected terrorists with links to Osama bin Laden has been botched by a flawed electronic surveillance system.

According to internal US government documents the system, called Carnivore, failed on a number of occasions, including a specific case where rather than just catching emails relevant to the investigation it also intercepted hundreds of emails from people not suspected of any involvement.

An FBI technician was then "so upset" by the technology's failure to work, he deleted all the recovered emails, including those from suspects.

As well as causing great embarrassment, this gaffe could have more severe repercussions for the FBI. Unauthorised monitoring of civilians' communications is against the law in the US.

The documents were made public under the US Freedom of Information Act after privacy group Epic threatened to take the government to court in order to gain access to information about Carnivore.

Carnivore is the code name for the technology behind the US government's surveillance of internet traffic and has been slammed by privacy activists who say it damages civil liberties.

David Sobel, general counsel for Epic, told a US newswire: "Carnivore is a powerful but clumsy tool that endangers the privacy of innocent American citizens. We have now learned that its imprecision can also jeopardise important investigations, including those involving terrorism."