USA Today cited a top federal law enforcement official on Wednesday as saying that the al-Qaida member had entered the United States, but “had to leave” shortly before 19 hijackers carried out the attacks.

“We are fairly confident we know who number 20 is,” said the official, involved in the September 11 investigation. He asked not to be identified.

The official would not say why the suspected al-Qaida operative left, whether he was alive or in US custody.

The newspaper reported that a top justice department official confirmed that the FBI believes it has identified the 20th hijacker.

Both officials said the FBI did not believe the suspect was accused al-Qaida conspirator, Zakaria Musawi or Ramzi bin al-Shaiba, the man suspected of coordinating the attacks.

Bin al-Shaiba tried to enter the United States at least four times before the attacks.

Musawi is the only person charged in the United States in connection with the hijacked plane attacks that killed some 3000 people.