What Really Happened The 9/11 Fact File

Conspiracy theories such as those popularized in the Internet documentary Loose Change are all the rage. Yet they are easy to refute, using new evidence from video and audiotape recordings, statements of captured al Qaeda members and the reports of commissions investigating the events.

First, there were warnings: In July 2001, an FBI agent in Phoenix, Arizona, fired off a memo to two of the bureau's anti-terror experts, one based in New York, the other at headquarters in Washington. The agent expressed concern that Osama bin Laden was sending students from the Middle East to take aviation lessons in the United States. He recommended that a list of flight schools be compiled and their attendance records examined to determine which foreign students had signed up for courses.

The memo disappeared into a sea of red tape, only to resurface after the damage of September 11 had been done.

At the end of June 2001, the CIA warned that a "major strike," a "spectacular attack" could be in the works. There were hints, scraps of information and an assortment of clues, but no one who could piece together this deadly mosaic.

Intelligence and communications failures, particularly between the FBI and the CIA, are detailed in the 9/11 Commission Report, which runs to nearly 600 pages.

The U.S. Federal Emergency Management Agency (FEMA) has issued its own report about rescue operations at the World Trade Center (WTC) and the Pentagon. And the National Institute of Standards and Technology published an analysis in 2005 that explains the causes of the towers' collapse.

Many of the questions posed by 9/11 can be answered more thoroughly and precisely today, allowing quite a few of the conspiracy theories to be debunked.

For example, information made public in the spring of 2006 clearly shows that the fourth hijacked airliner, United's flight 93, was not shot down by U.S. fighter jets, notwithstanding the numerous Internet rumors. At the trial of the suspected terrorist Zacarias Moussaoui, the prosecution played the audiotape from flight UA 93's black box. It is a dramatic recording, but there is no evidence that the plane was shot down.

In this sense, 9/11 is no different from the assassination of John F. Kennedy, the fatal car crash of Princess Diana and Dodi Fayed or - for Germans - the suicide of politician Uwe Barschel. Conspiracy theories abound. Not everyone is willing to swallow the official version of events. Some are convinced that information is being suppressed - they allege cover-ups, secret plots. They seek to implicate the government. They chat away in the blogosphere. And every attempt to refute a theory by analyzing fresh information spawns a new generation of suspicions.

Still, U.S. officials have done their part to abet the conspiracy theorists. Until recently, when they released the entire film, only five still surveillance photographs of the plane hitting the Pentagon were in circulation. At first, the torrents of debris unleashed by the collapsing towers of the World Trade Center were described as harmless. Today, New York doctors are treating patients with pulmonary ailments accompanied by a serious, hitherto unknown type of cough.

The substantial amount of new information available now, five years after the attacks, is inviting a re-examination of the events of the day. Some findings merely confirm what we already knew, but add layers of fresh detail. Others shift the focus, including the exact role played by Osama bin Laden. And much is new, including the dramatic final minutes of UA 93.

How did the hijackers get past airport security?

Nine of the 19 hijackers aroused suspicions during airport screening. In the end, they were waved through. And even if their knives and box cutters had been discovered, passengers were permitted to carry blades measuring four inches or less at the time.

On September 11, 2001, airports were using a computer system called Capps. Its job was to automatically identify potentially dangerous passengers. But the system wasn't equipped to deal with the likes of the 9/11 hijackers. At the time, security officials assumed that the main threat came from terrorists who would plant a bomb on a plane but not board themselves. Capps was programmed to detect people who survived the attack - and subsequently needed to cover their tracks. One of Capps' methods was to identify passengers who had paid for their tickets in cash, rather than by credit card.

Two of the five hijackers on American Airlines flight 77, which crashed into the Pentagon, were flagged by Capps. An airline employee at the check-in counter logged a question about two others into the computer: one of the al-Hamsi brothers had an ID with an error, and both were exhibiting suspicious behavior. But none of the suspects underwent further security checks; that's not how the system worked. Instead, airport personnel had to ensure that the luggage was only loaded onto the plane after its owners had boarded. Once a passenger had taken his or her seat, officials assumed the individual was not a terrorist.

The metal detector did sound on three of the five hijackers on AA 77. Two of them were sent to another detector and then subjected to a personal security check with a handheld device. One security employee even performed a wipe test on Nawaf al-Hamsi's shoulder bag, looking for traces of explosives. None were found, and he was waved through.

Were the 19 hijackers on the passenger manifests?

One of the most abiding 9/11 myths centers on the fact that the passenger manifests for the four airliners (first broadcast by CNN) didn't contain a single Arab name, implying that the 19 suspected hijackers weren't on board. As a result, they couldn't have carried out the attacks.

In fact, though, CNN had only broadcast the names of the victims - the passengers and flight crew, not the names of the terrorists.

On September 13, 2001, the Boston Globe obtained a complete list of passengers for flight AA 11, which rammed the North Tower. Mohammed Atta was in seat 8D - in business class. Sitting across the aisle were Hollywood producer David Angell and his wife, Lynn, in seats 8A and 8B. The hijacker Abd al-Asis al-Umari sat in seat 8G, next to Atta. As the Globe's investigative report showed, the seats occupied by the other hijackers on the three other planes have been long known. Additionally, ground staff were able to identify most of the men.

Who was the missing 20th hijacker?

For a long time, the U.S. government had suspected the Frenchman Zacarias Moussaoui, who was recently sentenced to life imprisonment for his alleged role in planning the attacks. This June, a website with ties to al Qaeda floated its own version, claiming that a Saudi named Turki al-Muteiri was to have taken part in the kamikaze mission. He wasn't on board any of the planes because the date for the attack was brought forward. Muteiri died during a 2004 gunfight in Riyadh.

Is Mohammed Atta's will authentic?

Yes. Abdelghani Mzoudi, one of the Muslims who witnessed the will, confirmed its authenticity to SPIEGEL. Suspected of aiding the terrorists, he was tried by a Hamburg court but acquitted. He then left Germany for Morocco.

Have the hijackers been positively identified?

Three of the hijackers on board the two planes that hit the World Trade Center have been positively identified. The FBI collected enough evidence from their rental cars and hotel rooms to create DNA profiles of all 10. Because the FBI coded these DNA profiles simply as "K" ("knowns"), medical examiners were able to positively identify the hijackers, but unable to attach names to the remains.

The FBI has not disclosed which of the 10 hijackers have been identified. Robert Shaler, the head of the medical examiner's team, believes that the three must have been in the rear of their plane when it hit the tower. "I still doubt the pilots have anything remaining to collect or analyze. Likely they were vaporized along with many of the innocent victims," he has written.

The nine hijackers on the other two planes have been identified as well - not by DNA analyses, but by a process of elimination: DNA was obtained for the crew members, Pentagon employees and other passengers (using toothbrushes etc. provided by relatives). Anything that couldn't be matched with these samples was assumed to be from the hijackers.

How were the hijackers armed?

During the trial of the suspected terrorist Zacarias Moussaoui, prosecutors submitted exhibit GX-FO08301, a box cutter: yellow plastic, with a black curved handle, made in China. It had been found in a rental car left by the terrorists at the airport in Washington. A superpower brought to its knees by assailants with box cutters - at least that's the story.

In fact, most of the hijackers were armed with regular knives. A passenger on flight AA 77, which smashed into the Pentagon, made the only reference to "knives and box cutters" during a phone call. Cell phone users from other planes said only that someone had been stabbed, but they didn't identify the weapon. Credit card records reveal that the hijackers bought everyday knives in at least two cases.

Inside the cabins, the terrorists also used pepper spray or other noxious chemicals. On three of the four flights, the hijackers claimed they had bombs on board.

Where and how were the combatants among the hijackers trained?

Abu Turab al-Urduni, a Jordanian al Qaeda veteran, was assigned this mission. Ten of the hijackers were trained at the al-Matar and al-Faruk camps in Afghanistan at the turn of 2000/2001, according to the director of al Qaeda operations, Chalid Sheikh Mohammed. The training included English, bodybuilding and techniques to disarm aircraft or security personnel. All ten had to slit the throat of a sheep and a camel using a Swiss Army knife.

What was the greatest risk for the operation?

According to Chalid Sheikh Mohammed, it was bin Laden himself. Months before the attacks, bin Laden apparently failed to maintain any operational security. In the summer of 2001, he repeatedly predicted a major attack on the United States. Mohammed and an associate urged bin Laden to show more discretion.

Had September 11 always been the date for the planned attacks?

No. Osama bin Laden actually wanted to strike earlier. May 12, 2001 - exactly seven months after the attack on the USS Cole - was one proposed date. Then, he got wind of a visit by Ariel Sharon, Israel's former prime minister, to the White House that summer. Sheikh Mohammed said he was able to talk him out of it both times, explaining that the teams weren't ready yet. Bin Laden reportedly became so impatient that he suggested simply crashing the hijacked planes rather than flying them into buildings.

Were the hijackers all fanatics?

Not to judge by their lifestyles. While Mohammed Atta was particularly devout and abstemious, another of the pilots - Ziad Jarrah - enjoyed partying and the occasional beer. Much to the chagrin of his accomplices, he even had a German-born Turkish girlfriend: Aysel S. This relationship troubled al Qaeda leaders until the very end. As a result of this relationship, they considered Jarrah the least dependable member of the group. Jarrah may have considered abandoning the plot and returning to Aysel. But just before the attacks, he chose death over love. On the morning of the flight, he called his girlfriend in Germany to bid farewell and told her he loved her three times over.

How was CNN able to provide live coverage so soon after the first plane had hit the North Tower?

It took three minutes for the world to be told of the catastrophe unfolding on September 11. Flight AA 11 rammed the North Tower at 8:46 a.m.; CNN broadcast the first live shots of the burning building as "breaking news" at 8:49 a.m. with the headline "Plane crashes into World Trade Center tower." The footage was shown simultaneously on CNN's 800 international affiliates.

The instant live coverage is easily explained: CNN had installed fixed cameras at various New York landmarks to provide scenery for live stand-up spots. The World Trade Center was a favorite interview backdrop for CNN Financial News, a nowdefunct CNN subsidiary. The camera that captured the burning North Tower was located two miles away on the roof of a skyscraper.

Why did the towers fall so quickly?

The engineers and fire-prevention experts agree on one thing at least: Both towers would have remained standing much longer had the fireproof coating on their frames not been destroyed in the crashes. Whether they would have survived completely remains a matter of debate.

A May 2002 study by the Federal Emergency Management Agency (FEMA) concluded that the towers had been structurally sound, and that the builders could not be held liable for their collapse. In 1973, when the buildings were completed, they were designed to withstand the impact of a Boeing 707. But 28 years later, the two Boeing 767s that hit the towers were traveling at 475 and 590 miles per hour, respectively, generating considerably more kinetic energy than a lone 707.

A 2005 report by the National Institute of Standards and Technology (NIST) blamed the damaged fireproofing for the catastrophe. Fires weakened the steel frame that supported the weight of the building. This caused several sections of flooring to sag. Unable to withstand the weight of the floors, the steel structures first buckled inward and then caved in completely.

Skeptics doubt that the blaze was hot enough to melt steel. They argue that jet fuel burns at a maximum of about 800 degrees Celsius. To melt steel, at least 1,500 C is required. As a consequence, they argue, fire could not have caused the collapse.

But steel doesn't have to melt completely. At 650 C, it loses 50 percent of its tensile strength. At just below 1,000 C, it loses about 90 percent, according to experts. Moreover, specialists believe that flammable materials inside - such as carpets, curtains, furniture and plastics - helped increase the temperature at the top of the towers to almost 1,000 C.

Why, despite being hit second, did the South Tower collapse first?

Although it was hit 17 minutes earlier, the North Tower remained standing for 29 minutes longer than the South Tower - for two reasons. As AA 11 impacted the North Tower 16 stories higher, there was less weight for the frame to support. And AA 11 was also flying more slowly and therefore caused less immediate damage.

Could the towers have been blown up?

Some critics still maintain that the Twin Towers could not have collapsed simply as the result of fire damage. They argue that the buildings must have been demolished. Indeed, television pictures do show minor explosions as the structures collapse.

The report issued by the National Institute of Standards and Technology (NIST) offered this explanation: Pieces of the planes sliced open the utility shafts inside the towers, enabling jet fuel to spread throughout the building. Explosions occurred whenever a spark ignited the fuel.

Beyond this, demolishing two buildings the size of the Twin Towers would have been a massive undertaking. With so many people involved, could it really have been kept under wraps?

Why wasn't anyone rescued from the roof?

Just minutes after the first tower was hit, police helicopters were already circling the World Trade Center. But smoke was streaming out of the North Tower, blanketing all but one small section of the roof. Additionally, the North Tower's roof was a dense forest of satellite and telecommunications masts, leaving no room for a landing pad. In theory, however, helicopters could have used rescue baskets.

The World Trade Center had already been the target of a terrorist attack in 1993, when police successfully airlifted dozens from the rooftops. But more than 10,000 had managed to escape via the staircases. Afterward, fire officials accused the police pilots of "showboating." Based on the experiences of the first attack, they argued it was more efficient to evacuate the building via the stairwells than to direct people to places where they would need to wait for help. Since the 1993 attack, massive steel doors had prevented access to the roof. An emergency services unit on the 22nd floor could have opened the doors, but communications with the top floor had been cut.

Helicopter rescues were impossible at the South Tower as well: the roof was completely obscured by thick smoke until its collapse.

How many people jumped?

Some leapt holding hands. Others fell alone. The desperation that made these people choose certain death is beyond imagination. Out of respect for the victims, many publications elected not to print images of the "jumpers." As a result, a sound recording remains the most chilling document of their deaths. A cameraman in the lobby of the World Trade Center filmed the horror-stricken expressions of the firefighters while his microphone picked up the dull thuds of the bodies hitting the ground.

In 2004, in an attempt to ascertain how quickly the fire and smoke had spread, NIST experts using video footage determined when and where people had leapt from the building. According to this and other studies, more than 200 jumped to their deaths.

Was the debris examined?

One tiny shard of glass about the size of a matchbox is all that remains of the Twin Towers' 43,000 windows. The rest were vaporized or pulverized. The collapse turned the two towers into 1.6 million tons of steel, rubble and dust. In an operation lasting months, the debris was shipped from Manhattan to New Jersey and deposited at a former landfill called "Fresh Kills." Piece by piece, rescue workers and investigators scoured the site for clues - body parts, fragments of bone, teeth or personal items. The energy unleashed by the collapse of the towers is illustrated by the discovery of "meteorites": blocks a full meter thick containing concrete, iron rods, pieces of furniture and steel matting from the buildings' flooring - all melded together by the heat and pressure.

After they were analyzed, the towers' girders were cut up and recycled around the world. Steel from the World Trade Center may now be in currency as parts of bridges, cars and cans.

How toxic was the cloud of debris?

In January 2006, New York police officer James Zadroga died of respiratory failure due to ''granulomatous pneumonitis,'' or fatal scarring of the lungs by hazardous material. Part of the 9/11 rescue effort, Zadroga was the first person whose death was officially linked to the debris and smoke at Ground Zero. The asbestos from the towers, pulverized cement and fiberglass, dioxin, PCB, the toxins from 50,000 vaporized computers, along with the diesel fuel from the excavators, have left some 15,000 people suffering from respiratory problems or the so-called WTC cough. A class-action suit has been filed against the Environmental Protection Agency (EPA) by local residents and the parents of schoolchildren: shortly after the attacks, its director had suggested that residents return home and schools reopen, arguing that the air in Manhattan did not represent a health risk.

Additionally, a suit against the City of New York has been brought on behalf of 8,000 firefighters who claim they were given inadequate breathing equipment for use at the World Trade Center site.

Were the flight data recorders of the WTC aircraft ever recovered?

The 9/11 Commission Report puts it succinctly: "The CVRs and FDRs from American 11 and United 175 were not found." Even before the report's release, experts expressed doubts about the recorders' ability to survive the crash into the towers, the ensuing fire, and finally the buildings' collapse. But thanks to statements made by firefighter Nicholas DeMasi, the whereabouts of the flight data recorders remains one of September 11's unresolved mysteries. In his 2003 book, DeMasi claimed he found three of the four black boxes at Ground Zero during October 2001.

DeMasi's assertions gained further credibility in December 2005 when the magazine CounterPunch quoted an anonymous source from the National Transportation Safety Board (NTSB): "Off the record, we had the boxes," the source said. "You'd have to get the official word from the FBI as to where they are, but we worked on them here."

Unfortunately, the source's identity remains a secret. But it is unlikely that three of the four black boxes would have been found during a single search at a time when the rubble of Ground Zero was still smoldering.

To this day, the FBI and the NTSB deny that the boxes were recovered.

Who was the woman in this picture?

The photograph shows the area where the plane struck the North Tower. A woman is visible near the bottom edge - on about the 97th floor. She is holding on to a severed pillar, waving. The picture conveys the utter despair of those trapped inside.

Numerous websites identified the woman as Edna Cintron (46), an employee with the insurance brokers Marsh & McLennan. Cintron's husband reportedly confirmed her identity.

Because Cintron was standing at the point of impact, some bloggers have assumed that the heat couldn't have been sufficiently intense to melt the steel inside the building. Cintron's photo ostensibly supports the hypothesis that the towers were intentionally blown up.

This is, of course, nonsense. Telephone calls made by victims show that not all the offices on the floors hit by the planes were destroyed immediately. Nor was the temperature consistent throughout each floor. Some of the trapped reported that they had fled to cooler areas - and the areas where the fire was sucking in fresh air were coolest of all, i.e. at the points where the aircraft had breached the walls.

Most likely, hardly anything about this story is accurate, even the woman's name; there is no evidence to substantiate her identity. Her husband, who reportedly recognized her, has discussed his wife's death in several interviews without ever referring to the picture. None of her colleagues, including the company's own memorial site on the Internet, has mentioned the photo. The only certainty is that the real Edna Cintron was not among the survivors. Nobody knows if she is the mystery woman in the picture.

Why did WTC 7 collapse?

The 47-story World Trade Center 7 building burned for seven hours beside the rubble of the Twin Towers - before collapsing in just eight seconds at 5:20 p.m.

FEMA's 2002 investigation concluded that WTC 7 had sustained comparatively slight damage prior to caving in. The 9/11 Commission made no mention of WTC 7 in its findings. And when the authorities remain silent or withhold information, rumors are guaranteed. Didn't the structure collapse a little too neatly? Could it have been dynamited?

The collapse of WTC 7 is currently being reviewed by the National Institute of Standards and Technology. Its experts believe that the building suffered far more damage from the plunging towers' rubble than had previously been assumed, particularly on the south side, the upper floors and the southwestern corner.

NIST's experts also attribute the building's ultimate collapse to the unusually heavy load borne by its individual supports. The buckling of a single support could have brought the entire structure down. The institute has found no evidence to suggest that bombs, missiles or explosives caused the building to cave in.

The final report has already been postponed several times. It is now due to be released this year.

How did the plane fit through the hole?

The hole that the Boeing 757 drilled in the Pentagon's exterior wall was some 10 yards narrower than the airliner's width. Just how credible is the assertion that flight AA 77 really did crash into the building? And if the damage could not have been caused by a Boeing 757, could a cruise missile have been responsible?

Conspiracy theorists like the Frenchman Thierry Meyssan maintain that a silhouette of the smashed plane should have been visible on the building's façade - an assumption refuted by physicists, who say that the remains of the plane after impact would have acted like a solid object rather than a fluid. Eyewitness accounts reveal that part of the right wing came off when the plane struck a huge generator in front of the building. The plane's left wing was smashed by the façade's support pillars.

The cruise-missile theory is also discredited by the various eyewitnesses who saw a jetliner crash into the Pentagon. What is more, the remains of the plane's crew and passengers have been identified.

Another obvious question presents itself: If flight AA 77 didn't smash into the Pentagon, where is it today?

Where is the wreckage from flight AA 77?

Hardly any aircraft parts are visible on photographs of the crash site at the Pentagon - according to skeptics, further evidence that a plane didn't hit the Pentagon.

But eyewitnesses who rushed to the scene reported seeing sections of the aircraft scattered widely throughout the vicinity of the crash. These included the nose, a tire, parts of the landing gear and fuselage, a cockpit seat and even a chunk of the tail with the plane's number on it.

There is no secret about the fate of the wreckage. On September 12, the Washington Post reported that a column of 50 FBI agents had marched shoulder-to-shoulder across the south grounds of the Pentagon, "picking up debris and stuffing it into brown bags. The lawn was scattered with chunks of the airplane, some up to four feet across," the newspaper reported.

Both of the plane's black boxes were also recovered. And all but one of the passengers on board flight AA 77 were positively identified - using remains recovered from the scene.

What is visible on the Pentagon videos?

In contrast to the attacks on the WTC, there is no live broadcast footage of the Pentagon crash. Until this spring, only five still photographs taken by a nearby security camera had been released. The photos showed only the fireball and not the plane, causing conspiracy theorists to believe that the administration had something to hide. The complete videos were released in May. A still shows an object approaching at high speed; the image is very blurred. Those who continue to believe that the United States attacked its own Defense Department will continue to maintain that the shape is a cruise missile.

After the crash, the FBI seized 85 security videos from the area. Legal proceedings to compel the FBI to release the videos are currently under way. It is unlikely that the footage would yield new information anyway as - according to an FBI official - most of the cameras weren't even trained on the Pentagon. She also stated that few cameras had captured images of the building after the attack, and just one had recorded the impact - as allegedly proven by the recently released film.

How were the inexperienced hijacker pilots able to hit the Pentagon with such accuracy?

The World Trade Center was a relatively easy target. Situated on the southern tip of Manhattan, it would have been instantly recognizable on the horizon. While the Pentagon is also a gigantic structure, it is relatively flat. As a result - as the black box has revealed - the pilot first entered Washington's Reagan National Airport as his destination in the plane's onboard computer. Nearly nine minutes before the crash, he switched off the autopilot.

From that point, the hijackers flew the plane manually, using the joystick and thrust control. Because the plane was still too high for a direct run at the Pentagon, they started a 330-degree turn five miles away. This is not difficult to accomplish and took about 2.5 minutes to complete.

It can be assumed that the terrorists were content to hit any part of the building. Their approach was tantamount to a controlled crash landing, a maneuver that can be practiced with any flight simulator software.

How could the passengers make phone calls from the planes?

Ten passengers and two crew members made phone calls from flight UA 93 before the Boeing 757 plunged into a field in Shanksville, Pennsylvania. Given the widespread belief that cell phones are all but useless at heights of over 8,000 feet, rumors were soon circulating that the calls had been faked.

It is difficult but not impossible to use mobile phones at such high altitudes. Numerous factors determine whether connections can be made and maintained. The odds improve when a plane is over a city or transmitter, or - at least with the latest cell phone generations - flying relatively slowly or at low altitude. Older phones with more powerful receivers - used for analog networks - frequently function at altitudes of 45,000 feet. These older models were relatively common in the United States until recently.

In any case, few of the calls from flight UA 93 were made using cell phones; the majority came from units built into the aircraft's seatbacks.

What happened during the final minutes of United Airlines 93?

UA 93 was the flight where the passengers tackled their hijackers - but they didn't regain control of the flight deck, as had initially been believed. This conclusion is supported by the voice recording played at Zacarias Moussaoui's trial this past spring.

The recording begins at 9:31 a.m., just a few minutes after the hijacking starts. A man, believed to be Ziad Jarrah, says: "Ladies und Gentlemen, this is the captain. Please sit down. Remain seated. We have a bomb on board. So sit."

A little later, someone calls out: "Go ahead. Lie down, lie down, down, down, down," followed by the voice of a crew member: "Please, please, don't hurt me." And a few seconds later: "I don't want to die."

At this point, the passengers hadn't taken any action. But the phone calls show that they were planning to rush the cockpit.

It is difficult to make sense of some of the recording. Many passages are unintelligible; there are scraps of Arabic such as "in the name of Allah" or "Allah is great." The cockpit door appears to be locked.

At 9:58 a.m., the hijackers realize that their guard at the door is being attacked: "Is something going on? A fight? Yes."

A passenger calls from outside: "In the cockpit, in the cockpit."

Then another voice in Arabic sounds from inside the cockpit: "They want to get in here. Hold the door, hold it from the inside. Hold it from the inside. Hold."

Apparently, the passengers were trying to ram the door open with a service cart.

And in the cockpit, the hijackers are screaming: "Is it over? Should we finish things?"

"No, not yet."

"When they all come, we finish things."

"Oh Allah."

A passenger calls out: "In the cockpit. If we don't, we'll die."

"Allah is the greatest."

"Cut off the oxygen. Cut off the oxygen."

"Down, down. Pull it down. Pull it down."

From 10:03 a.m. onward, the recording consists of nothing but cries of "Allah" with one single "no" in between. Nine seconds after 10:03 a.m., the recording stops.

Why were there no bodies, no wreckage and no large crater from UA 93?

The crater from the crash near Shanksville is remarkably small. Pictures taken at the site revealed little in the way of wreckage or body parts. Even today, the town's mayor is quoted as saying that he didn't see a plane at the crash site.

In reality, UA 93 was smashed to smithereens by the force of the impact. Still, rescuers did find several substantial pieces of wreckage, including sections of the fuselage. Photos of it were submitted as exhibits in Moussaoui's trial. Body parts were also found at the site, and identified using DNA analysis. Eight months after the crash, 125 volunteers conducted a new search of the area, and found additional pieces of wreckage: metal and wiring. They also collected bucketloads of human remains.

For the record, the mayor was misquoted. He had said that there was virtually nothing left of the aircraft; not that there was no evidence of a plane at all.

Why did George W. Bush stay sitting in the classroom for so long?

Two minutes after flight UA 175 barreled into the South Tower of the World Trade Center, White House Chief of Staff Andrew Card whispered the news into the president's ear: "A second plane has hit the second tower. America is under attack."

President Bush didn't say a word, didn't even ask Card for more information. Nor did he issue any instructions. Instead, he remained seated in the classroom for five to seven minutes and listened to the children read aloud from the book My Pet Goat. Bush's press secretary, Ari Fleischer, held out a sheet of paper with the words: "DON'T SAY ANYTHING YET."

Around 9:15 a.m., Bush finally stood up, praised the children and left. He went to another room and asked for details.

Karl Rove, a key adviser to the president, later told the ABC television network: "The president thought for a second or two about getting up and walking out of the room. But the drill was coming to a close and he didn't want to alarm the children."

Bush told the 9/11 Commission that he forced himself to remain calm because he didn't want the American people to see a distraught president in a time of crisis.

It remains unclear why he didn't leave the school immediately. Instead, he even made a brief statement before he left. The visit to the school was publicized on September 7. Had Bush been a terrorist target, the children would have been in grave danger.

Allegedly, as the Commission later reported, no one on Bush's staff had been aware that two other planes were missing at the time. Accordingly, Bush didn't learn of the attack on the Pentagon until he was en route to the airport.

Why didn't the CIA share its information on the terrorists with the FBI?

In its report, the 9/11 Commission cited 10 opportunities to track down bin Laden and his cohorts before September 11. With hindsight, these were the 10 mistakes that enabled the attacks.

In January 2000, for instance, the CIA failed to inform the FBI that Chalid al-Midhar, one of the budding hijackers, had a valid U.S. visa, the report said. In March 2000, it failed to pass on information that Nawaf al-Hamsi, one of the hijackers in the plane that hit the Pentagon, had flown to Los Angeles on January 15, 2000. In January 2001, the CIA failed to tell the FBI that Chalid, aka Taufik al-Atasch, one of the terrorists behind the attack on the USS Cole, had met Midhar and Hamsi in Kuala Lumpur. The two intelligence services worked in parallel - independently of and seemingly at odds with each other. After the 9/11 Commission's report had been released, its chairman Thomas Kean stated that neither Bill Clinton nor George W. Bush had been "well served" by the CIA.

In 1995, the U.S. Justice Department had tried to regulate the flow of information between agents and investigators, a practice that became known as "the Wall." The CIA didn't inform the FBI because it didn't want to endanger "sensitive sources." As a result, a memo headlined "Islamic Extremists Learn to Fly" landed on the desk of CIA director George Tenet, and no one at the agency understood its significance.

The CIA and FBI, former national security adviser Condoleezza Rice told the 9/11 Commission, had competed with each other and rarely cooperated. Her term was "systemic failure."

Why didn't U.S. air defense systems work on September 11?

The U.S. air defense network operates under the aegis of the North American Aerospace Defense Command (NORAD). At the end of the Cold War, the number of planes available to NORAD was reduced. On September 11, 2001, seven response centers were operating, each with two combat-ready interceptors.

All four hijacked planes fell under the jurisdiction of the Northeast Air Defense Sector (NEADS) which was based in Rome, New York. Commanders could therefore call upon just two response centers and only four mission-ready fighter planes.

Emergency management entails a long bureaucratic chain of command. The prevailing assumptions were that any hijacked planes would be easy to locate, that there would be enough time to analyze the situation, and that hijackers would issue demands and thus be willing to negotiate.

Because the air traffic controllers didn't completely understand the first radio communication from AA 11 and because news of the hijacking worked its way up the air traffic control system hierarchy so slowly, valuable minutes were lost. It was only after an air traffic controller in Boston heard a third radio communication at 8:34 a.m. ("Nobody move, please. We're going back to the airport. Don't try to make any stupid moves."), that the military was alerted. But officials placed their first call to Atlantic City, whose response center had been defunct for some time. As a result, military commanders at NEADS did not learn that flight AA 11 had been hijacked until 8:37 a.m. - 9 minutes before it sliced into the North Tower.

The air defense unit only learned by chance about flight AA 77, which smashed into the Pentagon, when an employee at the national air traffic control center casually mentioned that they had also lost track of that flight.

By then, it was 9:34 a.m. When three fighters took off from Langley Air Force Base in Virginia, they headed east. Five years later, no one has been able to explain why. In fact, when the plane struck the Pentagon at 9:37 a.m., the Langley aircraft were 150 miles from Washington.

The 9/11 Commission Report said that the defense of U.S. air space was not performed in compliance with the existing procedures: "What ensued was a hurried attempt to improvise a defense by civilians who had never handled a hijacked aircraft that attempted to disappear, and by a military unprepared for the transformation of commercial aircraft into weapons of mass destruction."

Did investors speculate on the attacks?

A few days after 9/11, there were indications that advance notice may have existed of the attacks. Some investors seem to have been expecting oil and gold prices to rise, and also purchased "put" options on stock of reinsurers for both American and United airlines (investors buying put options profit if the value of the stock falls). One buyer pocketed nearly $5 million on 4,744 puts on United stock purchased just four days before the attacks.

A closer look at the trading reveals that this was normal speculation. Both airlines had themselves churned out enough bad news to make investors pessimistic about their stock prices. On September 7, American Airlines issued a profit warning. On September 10, Goldman Sachs announced that it was again lowering its earnings forecast for AA. According to the Commission, the ostensibly suspicious purchase that same day of 4,516 put options was primarily due to a recommendation made in an investors' newsletter on September 9.

Apart from that finding, the profits made provide the strongest argument against any insider dealing. If someone did in fact have advance knowledge of the attacks, why did he or she invest such a small sum?

Was the White House under threat?

Exactly where the hijackers on flight UA 93 were heading remains a mystery. The most likely targets, however, would have been the White House and the Capitol, both in Washington, D.C. Abu Zubayda, an al Qaeda leader captured in March 2002 in Pakistan, has said the plane was slated to attack the White House. But investigators consider him an unreliable source.

Given its relatively small size, the White House would be difficult to hit from the air. Officials therefore consider the Capitol Building the more likely target. Given the plane's delayed takeoff from Newark, both the White House and the Capitol had already been evacuated by the time the plane crashed in Pennsylvania.

In February 2006, President Bush announced that al Qaeda had attempted to crash an airliner at the beginning of 2002 into Los Angeles' Library Tower, the tallest skyscraper west of the Mississippi.

Why didn't the NTSB investigate the cause of the crash?

The National Transportation Safety Board (NTSB) is an autonomous body that investigates all accidents involving civilian aircraft in the United States. It issues reports that attempt to determine the causality behind every accident.

But the NTSB has not figured in the alphabet soup of investigative committees, and skeptics blame the many unanswered questions on its continued exclusion - in their view, evidence of a cover-up. Had the NTSB completed an investigation, they argue, there would be no doubts as to whether flight UA 93 really did crash or was in fact shot down in Pennsylvania.

There is, however, a simple reason why the NTSB was not asked to investigate: When the U.S. Justice Department has reason to believe that an accident is attributable to criminal activity, responsibility may be delegated to another agency - in this case, the FBI.

How were the chief planners Ramzi bin al-Shibh and Chalid Sheikh Mohammed captured?

The most detailed account appears in the work of Ron Suskind, whose book The One Percent Doctrine apparently relied on information provided by senior CIA officials, including former director George Tenet. Mohammed's hideout near the Pakistani capital of Islamabad was actually disclosed by an al Qaeda operative who walked into the U.S. Embassy in Islamabad at the end of February. During a meeting, he told Tenet that he didn't care about the $25 million reward; nor was he motivated by the offer of a new identity and new home in the United States. "I want my children free of these madmen who destroy our religion and kill innocent people." He then reportedly asked Tenet whether President Bush knew what he had done. "I told him," the CIA director is quoted as saying. Suskind writes that bin al-Shibh was captured as a result of his meeting with al-Jazeera reporter Jusri Fuda. The CIA was apparently given details about the meeting not by Fuda, but by the emir of Qatar, whose family helps finance the news channel. It was, in Tenet's words, an "unbelievable gift." Tenet promised the emir that bin al-Shibh would not be seized until al-Jazeera had broadcast the interview. The emir was willing to take in stride suspicions that the broadcast had put the CIA on bin al-Shibh's trail, but nobody was to learn that he had effectively initiated the arrest by revealing internal newsroom information.

How was information obtained from bin al-Shibh and Mohammed?

Evidently, both were brutally tortured in secret CIA prisons aka "Black Sites." The methods included near-drowning, sleep deprivation, being left to stand in freezing rooms, and repeated death threats. In Mohammed's case, the CIA brass reportedly authorized any form of torture that would make him talk. Pulitzer Prize winner Ron Suskind has noted that the U.S. intelligence agency even threatened to harm Mohammed's seven-year-old son and nine-year-old daughter if he didn't talk. Reportedly, a similarly dire fate awaited bin al-Shibh. The CIA was keen to circulate fake documents demonstrating that the Yemeni was cooperating voluntarily - and even on the CIA's payroll. The idea was to incite al Qaeda supporters to exact revenge on his family.

Will the planners of the 9/11 attacks face trial in the United States?

Possible, but unlikely. Chalid Sheikh Mohammed and Ramzi bin al-Shibh apparently provided information only under duress, rendering their statements inadmissible in a court of law. In addition, the U.S. government would likely be sensitive to exposing its endorsement of torture. Nevertheless, during Zacarias Moussaoui's trial in May, U.S. prosecutor David Novak stated that other trials would follow, but that the two main plotters were still being interrogated: "They're going to face justice." Within U.S. government circles, there is a growing debate as to how the suspected mass murderers could be brought to trial - to remind Americans of al Qaeda's horrific attacks.

Why do doubts surround the official investigations into the events of 9/11?

For one thing, several major inquiries in the past have only revealed partial truths. Beyond this, major historic events always provide scope for speculation. President John F. Kennedy, assassinated by a lone gunman? Impossible! There must be more to it. The 9/11 attacks on the United States? Allegedly perpetrated by a bunch of Arabs with box cutters and rudimentary flight training. According to this logic, President Bush and Vice President Cheney exposed America to attack in order to justify the war plans they were hatching. They had missiles fired at the Pentagon, arranged for the World Trade Center to be dynamited, and ordered UA 93 to be shot down. Beyond the fact that most conspiracy theories aren't backed up by the evidence, simple logic can also be used to debunk them. To pull off such a staggering operation, an army of the complicit would be required: pilots, demolition experts, soldiers and air traffic controllers. With so many coconspirators, one of them surely would have talked by now.