Former FBI agent Ali Soufan says he has not been allowed to tell the truth about 9/11 and events since. A former FBI agent who worked at the heart of America's battle against al-Qaeda has told the BBC he is being prevented from telling the truth as he challenges the back story of 9/11 and what has happened since.
Mr Soufan also argues against the effectiveness of interrogation techniques used by the CIA, such as water boarding. Ali Soufan has not appeared on camera before, but he has now decided to speak out to counter what he sees as a misleading narrative about the last 10 years.
Mr Soufan has direct, first-hand experience of some of the most heated controversies of the past decade: whether 9/11 could have been prevented and whether tactics like the water boarding of al-Qaeda suspects were effective and justified.
Born in Lebanon, Mr Soufan came to America as a teenager and joined the FBI in the 1990s. As one of the only Arabic speakers he was assigned to early investigations on al-Qaeda.
When the 9/11 attacks occurred, he was in Yemen investigating the bombing of the USS Cole.
The day after the attacks, he met a CIA officer at the US embassy in Yemen. The officer passed him an envelope.
Inside was a report detailing links between people Mr Soufan had been investigating for the warship bombing and two of the hijackers - who had been living in the US for months. Mr Soufan says that written requests for this kind of information had been made three times before without any result.
"I think it was probably the worst feeling I have ever experienced in my life," he told BBC Newsnight in an interview.
"It was a combination of frustration, anger, sadness, betrayal. The only thing I recall is I left the office, went across the hall to the bathroom and I just threw up."