‘I think we’re confident that he was one of the key figures,’ said FBI director Robert Mueller on 6 June. Mohammed is reported to have been at the centre of operational planning for the attacks and to have known – unlike the hijackers – the entirety of the plot. The recent focus on Mohammed comes after he was named as the person who came up with the plan by captured Al-Qaeda commander Abu Zubaida.

Late last year, the FBI linked Mohammed to financial transactions that funded the attacks. He was already on the FBI most wanted list for his alleged involvement in the proposed plot to bomb commercial US airliners flying between the US and the Far East, and was indicted in 1996. The FBI is offering a reward of $25 million for information leading to his capture.