A man defending himself against a terrorist charge connected with the 11 September attacks is having difficulty proving his case, as the FBI can't track down his Hotmail account.

According to the Washington Post, Zacarias Moussaoui needs the email records from his xdesertman@hotmail.com account to back up his alibi about flying lessons he took in Minnesota.

But FBI officers claim that they can't find the account and have a certificate from Hotmail to prove it.

Hotmail's recently introduced policy of deleting all information in an account that has been dormant for 30 days, and its habit of recycling the user name after 90 days of inactivity, could be an explanation for its apparent non-existence.

Leonie Brinkema, the district judge investigating the case, is said to be sceptical about the FBI's failure to recover the email trail.

Moussaoui has demanded copies of emails he sent from various locations before his arrest. He was picked up in August 2001 on immigration charges after arousing suspicion while taking the flying lessons.

Judge Brinkema said in court that, given the intense law enforcement attention focused on Moussaoui after 11 September, she did not understand why an immediate and thorough investigation into the defendant's email and computer activities did not lead investigators to the Hotmail account, if it existed.

She ordered prosecutors to supply an affidavit from the FBI "explaining how and when, if at all, the FBI examined the contents of the defendant's computers", as well as other computers Moussaoui is seeking to have examined.

"The affidavit must indicate why investigators were unable to retrieve any information from MSN Hotmail and/or any other computers or accounts searched," said Judge Brinkema.

"It must make clear whether any efforts were made to obtain forensic expert services of any other government agencies such as the CIA or NSA to assist in retrieving the information."

The government said in court papers that agents tried to access Moussaoui's email accounts but were unable to do so.

A certificate filed by a Hotmail official maintained that the company had no record of Moussaoui's account.