From the archives: Who is Ali Soufan?

This week on 60 Minutes, Ali Soufan offers a warning: al Qaeda has continued to grow and get stronger, and there's a new bin Laden waiting in the wings.

"We killed Osama bin Laden, but his message lives," Soufan tells correspondent Holly Williams on the broadcast. The messenger, Soufan explains, is bin Laden's son Hamza, who is poised to become the next leader of al Qaeda.

Who is Ali Soufan? A Lebanese-born Muslim American, he was the only FBI agent based in New York on September 11th who spoke Arabic. He became the agency's lead investigator of al Qaeda after the attacks, and he's spent the last two years analyzing an unprecedented cache of documents seized in Osama bin Laden's compound.

Ali Soufan first appeared on 60 Minutes on the 10th anniversary of the September 11th attacks to talk about his role as an FBI interrogator. It was Soufan who helped gather the critical intelligence that linked al Qaeda to September 11th and identified Khalid Sheikh Mohammed as the mastermind of the attack. His two-part interview can be viewed in the player above.

In the months after the attacks, Soufan interrogated al Qaeda prisoners at secret locations all over the world. He was known for his ability to outwit terrorists, in part because he already knew so much about them. 

"The fact that maybe I understood the culture, the fact that I genuinely, as a person, have an interest in these kind of things, that probably helped me," he told correspondent Lara Logan in 2011.

Soufan also told Logan that enhanced interrogation techniques, such as waterboarding, were introduced in the middle of questioning the U.S.'s first high-value detainee, Abu Zubaydah. President Bush defended the techniques as necessary in an address to the nation in 2006, but Soufan told 60 Minutes they weren't effective.

"I think somebody told the president some fake information, some false information," Soufan said. "Zubaydah did not stop talking. Introducing the techniques made him stop talking."

Soufan also said that in the ten years after September 11th, he was anguished by the thought that the attacks could have been prevented, a sentiment he echoes on this week's broadcast.

"It won't be honest to say that, you know, I don't feel a sense of responsibility that this thing could have been stopped," Soufan tells Williams on 60 Minutes. 

During his earlier interview with Logan, Soufan explained in more detail why he feels that way. While Soufan's FBI team was investigating the attack on the USS Cole in November 2000, they learned that an al Qaeda operative had met with other terrorists in Asia and received a large sum of money. Soufan says he asked the CIA if it knew what this operative was doing through three formal requests for information. Soufan says the CIA replied, telling him the agency didn't know anything.

But Soufan says he later learned the CIA knew eight months before September 11th that this same operative had met in Malaysia with two terrorism suspects who would later hijack the plane that crashed into the Pentagon. And the CIA also knew that those two suspects were heading to the U.S.

Had Soufan's team received that information, things may have been different, he says.

"I try not to think about that," Soufan said. "I try not to think about what could have happened. Maybe, maybe thousands of American lives [would have been] spared, maybe."

Today Soufan is focused on preventing another attack like September 11th and believes unraveling the secret world of the bin Ladens is a crucial component.

According to this week's 60 Minutes report, Osama bin Laden's son Hamza was educated by the people who masterminded the East African embassy bombing and the USS Cole bombing, and they have been preparing him to become the new leader of al Qaeda.

Soufan believes the younger bin Laden is now hiding somewhere in Pakistan. 

"I think we're not done with the bin Ladens yet," Soufan says.