Five years before the worst terror attack in American history, a U.S.-educated Kuwaiti pitched an outlandish idea to Usama bin Laden (search). Khalid Shaikh Mohammed (search), now a U.S. captive, concedes his apocalyptic vision of 10 planes steered into nuclear power plants, skyscrapers and other American targets received only a lukewarm response from the Al Qaeda (search) kingpin.

The meeting in Afghanistan in mid-1996, however, apparently was the genesis of the attacks that killed nearly 3,000 people on Sept. 11, 2001. Three reports issued this week by the Sept. 11 commission provide the fullest picture yet of how Mohammed's idea evolved from wild scheme to unfathomable reality — and the government's chaotic response.

Mohammed had targeted U.S. airliners before. He was indicted in the United States earlier in 1996 for plotting to bomb 12 flights over the Pacific Ocean, but he wasn't captured. Mohammed, born in Kuwait and a 1986 graduate from North Carolina Agricultural and Technical State University, also wanted to crash a plane into CIA headquarters.

His new plan needed bin Laden's money and his muscle.

Between May 1996, when bin Laden moved to Afghanistan from Sudan, and the Sept. 11 attacks, more than 20,000 men trained at his terror camps. They learned to be soldiers and, the Sept. 11 commission said, "to think creatively about ways to commit mass murder."

They floated ideas: take over a Russian launch site and fire a nuclear missile at the United States, pump poison gas into a building's air conditioning, hijack a plane to attack a city.

Advanced terrorism training was given to only the most promising recruits, among them the Sept. 11 hijackers. Early in 1999, bin Laden gave the go-ahead for a scaled-down version of Mohammed's proposal three years earlier.

According to Mohammed, the two drew up a list of potential targets:

_the Capitol, perceived source of U.S. policy in support of Israel;

_the White House and Pentagon, both advocated by bin Laden as potent American symbols;

_the World Trade Center, favored by Mohammed, whose nephew Yousef was in prison for the 1993 bombing of the towers that represented America's financial might.

Bin Laden selected potential suicide hijackers. The first two arrived in Los Angeles on Jan. 15, 2000. During the next 18 months, 17 more followed, some entering the country on fraudulent visas. Four, including ringleader Mohammed Atta (search), attended U.S. flight schools.

FBI agents in Arizona and Minnesota were suspicious of the flight students, but their alarms went unheeded by higher-ups.

The summer of 2001 was a time of intensive preparation by the hijackers. They rode cross-country flights for surveillance, brought boxcutters onto planes as tests, practiced flying rented planes and honed their strength at gyms.

Meanwhile, in Afghanistan, senior Al Qaeda leaders were under pressure from the Taliban not to attack inside America's borders. Some feared U.S. military retaliation. Despite the pressure, bin Laden prodded Atta to get on with it.

In mid-August, Atta settled on the date of Sept. 11, choosing a week when Congress would be back from summer break. Bin Laden wanted to strike the White House; Atta preferred the Capitol as an easier target. The commission said it has been unable to determine definitely which was the intended target on Sept. 11.

The hijackers bought their flight tickets in late August and early September. Then, ever loyal, they took care of a final detail — sending back to Al Qaeda $36,000 they didn't need.

At the airports early on Sept. 11, nine of the hijackers were pulled aside for extra security screenings, but all were allowed to proceed, some with hidden knives and boxcutters.

At 8 a.m., American Airlines Flight 11 took off from Boston, with five hijackers aboard. Within 45 minutes, the other 14 hijackers were airborne: on flights out of Boston at 8:14, from Dulles airport near Washington at 8:20, from Newark, N.J., at 8:42.

On the ground, the first sign of trouble came when air traffic control lost contact with Flight 11 about 8:13 a.m. Minutes later, air traffic controllers heard an ominous transmission from the cockpit:

"We have some planes. Just stay quiet and you'll be OK. We are returning to the airport."

The Boston controller wasn't sure what he had just heard. Then came a second transmission, believed to have been the voice of Atta, the plane's pilot, addressing the passengers: "Nobody move. Everything will be OK. If you try to make any moves, you'll endanger yourself and the airplane."

It was a hijacking.

Air controllers first tried to call a military alert site in Atlantic City, N.J., unaware it had been closed. It was the start of a cascade of communications errors that morning that undermined any chance of stopping the attacks.

At 8:37 a.m., controllers reached the Northeast sector of NORAD, the North American Aerospace Defense Command, and urged them to scramble fighter jets because a hijacked plane was headed for New York.

"Is this real-world or exercise?" responded an incredulous military official.

"No, this is not an exercise, not a test," the FAA said.

Nine minutes later, Flight 11 flew into the north tower of the World Trade Center.

Those nine minutes were the most notice the military would receive of any of the four hijackings.

Confusion turned to chaos during the next hour, as the Federal Aviation Administration struggled with "an unprecedented challenge they had never encountered and had never trained to meet," the commission wrote.

Just before 9 a.m., President Bush stood outside a Sarasota, Fla., elementary school classroom, preparing to read to second-graders. Aides told him a small plane had struck the World Trade Center. He assumed it was a tragic accident, though the FAA and air defense officials already knew otherwise.

Air traffic controllers in New York were looking frantically for another plane that had disappeared from their screens. The hijackers had turned off its transponder, a tracking device.

"It's escalating big, big time," a New York manager warned the FAA command center in Herndon, Va. Two minutes later, United Airlines Flight 175 from Boston crashed into the south tower of the World Trade Center.

White House Chief of Staff Andrew Card whispered in the president's ear: "A second plane hit the second tower. America is under attack."

Bush stayed in the classroom another five minutes or so, listening to children read. He later said he was trying to project calm.

Bush wanted to return to the White House, but his aides and the Secret Service advised it was too dangerous. Air Force One took off about 9:55 a.m., its destination undecided.

The Secret Service just wanted to get him off the ground quick — on a day when death came from the air, the skies offered refuge.

Before Air Force One could lift off, the Pentagon was in flames from the crash of American Airlines Flight 77.

That plane, which had taken off from Dulles, deviated from its flight pattern, then disappeared from radar at 8:54 a.m. A controller in Indianapolis, who had been tracking it, was unaware of the first two hijackings and believed it might have crashed.

A half-hour later, air traffic personnel at Dulles airport spotted the plane moving east at an extremely high speed. An unarmed National Guard cargo plane, already in the air, was tasked to follow it.

Minutes later, at 9:38 a.m., came his report: "Looks like that aircraft crashed into the Pentagon, sir."

Bush reacted to the news by calling Vice President Dick Cheney from the air: "Sounds like we have a minor war going on here. I heard about the Pentagon. We're at war. ... Somebody's going to pay."

Meanwhile, air traffic control in Cleveland heard transmissions that sounded like screams and a struggle. Then a voice from United Flight 93: "Keep remaining sitting. We have a bomb on board."

The plane turned toward Washington.

As FAA higher-ups discussed whether military jets should be scrambled, the passengers and flight attendants took things into their own hands, improvising an assault on the hijackers.

In the White House's underground shelter, with reports of a jet closing in, Cheney authorized the Air Force to shoot down hijacked planes. Cheney said Bush earlier had given him the authority to do so.

The order, which came minutes after Flight 93 had crashed in a Pennsylvania field, never was passed on to the fighters circling Washington and New York.

The same National Guard pilot who witnessed the Pentagon crash, then resumed his flight to Minnesota, was the first to report "black smoke" on the ground in Pennsylvania.

Two hours after it began, an attack five years in the making was over. The last plane had been downed short of its target, not because of government action, but at the hands of its passengers.

"We are sure that the nation owes a debt to the passengers of United 93," the commission wrote. "Their actions saved the lives of countless others, and may have saved either the U.S. Capitol or the White House from destruction."