The Interrogator

Key to a successful interrogation -- being able to think quickly on your feet. How FBI interrogator Ali Soufan improvised a creative way to determine when one subject was lying.

Former FBI agent Ali Soufan says critical CIA intelligence about Al Qaeda was not communicated to the FBI. If that information had been shared, Soufan says, "The world would be very different today."

Al Qaeda operative Abu Zubaydah was captured in Pakistan in March 2002. FBI Agent Ali Soufan tells FRONTLINE he was able to convince Zubaydah to give up significant details about Al Qaeda plots. But, he says, cooperation dried up once the CIA stepped in with new "enhanced interrogation techniques."

One of only eight Arabic-speaking FBI agents, Ali Soufan explains to FRONTLINE why he believes the attacks on the World Trade Center could have been prevented and how the use of torture failed to produce actionable intelligence in, "The Interrogator," airing Sept. 13.

FBI agent Ali Soufan's biggest breakthrough -- identifying eight of the 9/11 hijackers began by confronting a source with some photos.

The objective is always the same -- getting actionable intelligence to use in the fight against Al Qaeda -- but different subjects require different types of tactics, explains former FBI interrogator Ali Soufan.

Listening to one Al Qaeda member's grievances leads to a big get for FBI interrogator Ali Soufan -- he turns a key figure who ends up being the star witness and convicting four Al Qaeda figures at the U.S. embassy bombings trial.