Osama bin Laden may still be at large, but the man captured in Pakistan last Saturday was even more important than bin Laden in the planning and execution of the Sept. 11 attacks.

Khalid Shaikh Mohammed was apprehended in his pajamas just before dawn in a suburban home near the Pakistani capital of Islamabad. American authorities will have many questions for him because as, Bob Simon first reported last fall on 60 Minutes II, Khalid Shaikh Mohammed was not only the mastermind of 9/11, but America's most lethal enemy for more than a decade.

Just how important he was in the campaign to bring America to its knees only started to dawn on U.S. investigators last spring. Around that time, a reporter for the Arabic news channel Al Jazeera was summoned to Pakistan for a meeting with the men on the inside.

Not only did Al Jazeera reporter Yosri Fouda interview Mohammed, whose role in the plot only became clear to American intelligence last spring, but he also spoke with Ramzi Binalshibh, Mohamed Atta's Hamburg roommate, who was originally slated to be one of the four pilots leading the attack.

Invited to Karachi by al Qaeda, Fouda was driven blindfolded – with several changes of cars – to an apartment where he met the two men.

"Immediately Khalid introduces himself as head of the military committee of al Qaeda," said Fouda of Mohammed, a Kuwaiti of Pakistani descent who has terrorized Americans since 1993.

According to Khalid, that committee actually was the arm of al Qaeda that decided to strike America inside America, and also chose the targets that were actually hit on Sept. 11.

As Fouda described it, Osama bin Laden is the chairman of the board, and Khalid Shaikh Mohammed is the CEO who gets things done. Mohammed has only been interviewed once in his life. His meeting with Foudra was his first - and possibly his last - with a reporter.

Unlike Mohammed, Binalshibh was ready to do an interview for broadcast. In it, he said, "I do not regret any of this whatsoever, for this is our path and the end is best for the righteous, Allah willing. We will persevere with this until Allah the Almighty, grants us victory, or takes us to him as martyrs."

Intelligence sources say Mohammed directed the first World Trade Center bombing, as well as a 1995 plot to down a dozen American airliners in the Pacific and crash a plane into the CIA headquarters. His operative in those plots was his nephew: Ramzi Yousef. But those attacks failed.

Ramzi was tracked down and later convicted. But Mohammed, a master of disguises who traveled the world unnoticed, disappeared. Then in 1996, word reached the FBI that he had surfaced in Qatar.

"We sent a team of FBI agents from this country, with the cooperation of the government of Qatar, to bring him back," says Neil Herman, who headed the FBI's investigation into the 1993 bombing. "For whatever reason, still remains a mystery, he found out that a team was en route and the rendition was unsuccessful. Unfortunately, our best opportunity was missed."

When Yousef was captured and jailed, Mohammed needed a new blueprint and a new master terrorist.

"You need a perfectionist if you are playing with America," Fouda told Simon. "And I think Khalid, for this reason, was lucky to find someone like Atta. With these qualities and at the same time with a lot of black smoke inside him."

The smoke had not turned black yet when a preppy-looking teen-ager known then as Mohamed El-Amir went to the American University in Cairo to learn English. The smoke started appearing in Hamburg, where the man we know as Mohamed Atta came to study city planning at a technical university. He was becoming increasingly religious and increasingly frustrated: he wanted to go back home to Cairo and get a job, but saw few prospects.

Atta grew a beard to show solidarity with Muslim fundamentalists in Egypt. He was looking for a cause, and Khalid Shaikh Mohammed was looking for a candidate. It was a perfect match.

Atta was recruited by al Qaeda at the Al Quds mosque, hidden in a non-descript building in downtown Hamburg. So was a Yemeni student, Ramzi Binalshibh. In 1998, Atta and Binalshibh became roommates in Hamburg. The cell was forming, and the nucleus was Mohamed Atta.

"This brother was amazing, extremely amazing," Binalshibh is heard telling Fouda. "I have never come across anyone from among the brothers that I know who was more eager than him to perform the night prayers, to the point where I remember the neighbors complain about his reading of the Koran at night."

By the end of November 1999, Atta, Binalshibh and two other future pilots were sent to Afghanistan to an elite al Qaeda camp. Khalid Shaikh Mohammed and his military committee had drawn up a new plan for America.

"The first thing that jumped into their minds, according to Khalid, was striking at a couple of nuclear facilities in America," said Fouda. "That, according to him, was later taken off the list for fear it might get out hand."

When he pressed them on this, Fouda said, they said they were unwilling to take that much risk "for now."

Instead, the operation would strike at symbols of America's military, political and economic power. When Atta arrived in New York in June 2000, he carried with him a report on potential targets made by reconnaissance teams that had been sent to the U.S. a year earlier.

"The White House, at that time, was on the list," Fouda said. "But one of the reconnaissance units went back and recommended that it should be taken out of the list for navigation reasons."

The Capitol took its place. At the top of the list was a site Khalid Shaikh Mohammed wanted to revisit with a vengeance: The Twin Towers. His new plan took elements of the World Trade Center bombing in 1993 and mixed them with the failed '95 operation to use American airliners as weapons.

"He said that during the meeting of his committee," Fouda reported, "they decided that the goal was to cause as many deaths as possible, to direct a big slap to America on American soil, in front of the world."

To deliver the slap, terrorists had to learn how to fly. By the summer of 2000, Atta and two of his comrades were looking for flight schools. Binalshibh reveals why they chose Florida.

"The prices in America were convenient and the weather was ideal for more flying hours, especially in the coastal states like Florida," Binalshibh said. "And the term of study wouldn't take long."

Binalshibh was supposed to join them, to become one of the four pilots. He applied for a U.S. visa four times, and was turned down four times. Kept off the front line, Binalshibh stayed behind in Hamburg and became the link between Atta in Florida and Khalid Shaikh Mohammed in Afghanistan.

In early 2001, a fourth pilot, a Saudi, was found to replace Binalshibh. Then, it was time to choose the hijackers, those who would actually take over the planes.

"About five months before the zero hour, the foot soldiers, or so-called muscles, were chosen," by Mohammed, Fouda said.

Khalid Shaikh Mohammed said his problem was that he had too many volunteers.

Mohammed told Fouda he plucked more than a dozen Saudis out of what he called the Department of Martyrs in Afghanistan. Each recorded a video before leaving for the U.S. The Saudis knew they were going to die; they just didn't know how.

As the Saudis were arriving in the U.S. in July, Atta was taking off, flying into Madrid and driving 500 miles to a Spanish coastal resort for a working vacation. Joining him was Binalshibh with a message from Khalid Shaikh Mohammed. The final date for the operation was in Atta's hands. Atta had Shaikh Mohammed's complete trust.

Then, on Aug. 29, the phone rang in Binalshibh's Hamburg apartment at three in the morning.

It was Atta with an important, but cryptic message: "He said to me, 'One of my friends related a riddle to me and I cannot solve it, and I called you so that you can solve it for me.'" Binalshibh is heard saying.

Atta goes, "Two sticks, a dash and a cake with a stick down."

Binalshibh said, "I said to him, 'Is this the riddle? You wake me from a deep sleep to tell me this riddle? Two sticks and I do not know what?'"

Eventually, Fouda says, Binalshibh realized what Atta meant. So he says to him, "OK. Tell your friend, he has nothing to worry about. It's such a sweet riddle."

Binalshibh explained it: "The two sticks represent the number 11, then the dash, and then the cake from which a stick dangles represents number nine. Thus, the picture becomes complete: the 11th of September."

Binalshibh left Hamburg on Wednesday, Sept. 5, for Pakistan. From there, he sent a messenger into Afghanistan with news for Khalid Shaikh Mohammed and Osama bin Laden: Tuesday, Sept. 11, would be the day.

In America, Atta, the city planner, was getting ready to destroy a city, getting ready to finish the job Khalid Shaikh Mohammed had started years before.

Even when he saw the carnage, Binalshibh, in Pakistan, felt no remorse: "No sane Muslim doubts that the operations of the blessed day of Tuesday, on the 11th of September in Washington and New York, was one of the glorious days of the Muslims," he said.

In fact, both Binalshibh and Shaikh Mohammed had hoped for a much higher death toll. Even so, they want history to record what they did accomplish.

Binalshibh gave Fouda a manifesto justifying the attacks in the name of Allah, and asked him to hand it over to the Library of Congress.

Now, it seems, Binalshibh will get all the recognition he wants - in an interrogation room.

His brazenness caught up with him and, on Sept. 11, 2002, his voice on the audiotaped interview was matched to a phone call.

Exactly a year to the day after the 9/11 attacks, he was arrested in Karachi.

That arrest tightened the noose. And last Saturday morning, Khalid Shaikh Mohammed received a wakeup call. Osama bin Laden may still be at large, but al Qaeda may never be the same.

