9/11 Attacks: How Al Qaeda Planned the Plot and What Happened on September 11

The images remain etched into history: two hijacked planes slicing through the Manhattan skyline and crashing into the World Trade Center, smoke billowing over the Pentagon, and a shattered field in Pennsylvania.

Twenty-five years ago, on September 11, 2001, 19 al Qaeda terrorists hijacked four commercial aircraft and turned them into weapons in the deadliest terrorist attack on US soil. Three planes struck the World Trade Center in New York and the Pentagon near Washington, while the fourth crashed into a field in Pennsylvania after passengers attempted to regain control.

A total of 2,977 people were killed, excluding the 19 hijackers, according to US government records.

But the story of 9/11 began years before the first aircraft struck its target.

How the 9/11 Plot Began

Osama bin Laden, founder and leader of al Qaeda, was ultimately held responsible for the attacks. The 9/11 Commission traced the organisation’s campaign against the United States through the 1993 World Trade Center bombing, the 1998 US embassy bombings in Kenya and Tanzania, and the 2000 attack on the USS Cole.

The 1998 embassy bombings marked a major turning point. The CIA says Khalid Sheikh Mohammed, later identified by the 9/11 Commission as the principal architect of the attacks, received bin Laden’s approval to plan attacks inside the United States less than six months later.

Khalid Sheikh Mohammed had long considered using aircraft as weapons. The 9/11 Commission identified him as the principal architect and manager of the so-called “planes operation”.

The 19 Hijackers Were Not One Single Group

The hijackers came from different backgrounds, although the plot relied heavily on an al Qaeda cell based in Hamburg, Germany.

Mohamed Atta, Marwan al-Shehhi and Ziad Jarrah became three of the four pilot-hijackers. Hani Hanjour was the fourth.

The remaining 15 were described as “muscle hijackers”, whose role was to overpower passengers and crew and help seize control of the aircraft.

The men travelled through several countries before entering the United States. Several passed through the United Arab Emirates, where al Qaeda facilitators helped arrange tickets, traveller’s cheques and hotel stays.

The 9/11 Commission found that 14 of the 15 muscle hijackers had entered the US by the end of June 2001, with most travelling on tourist visas.

Hijackers Had Already Triggered Security Alerts

Some of the hijackers had already attracted attention from US airport security systems.

Mohamed Atta was flagged before his flight from Portland, Maine, to Boston. Three other Flight 11 hijackers were also flagged in Boston. However, the alerts generally resulted in additional baggage checks.

At Washington Dulles International Airport, several Flight 77 hijackers also triggered security alarms.

Khalid al-Mihdhar and Majed Moqed set off metal detectors, while Nawaf al-Hazmi triggered two alarms, was screened with a hand-held detector and had his carry-on bag checked for explosives.

All five were nevertheless allowed to board. The 9/11 Commission later described the screening of Moqed and Hazmi as “marginal at best”.

Warning Signs Before September 11

US authorities had received repeated warnings that bin Laden and al Qaeda were planning attacks against the United States.

The 9/11 Commission later concluded that by the summer of 2001, “the system was blinking red.”

On August 1, the FBI warned that an attack inside the US could not be ruled out. Two days later, another intelligence warning said the threat of an al Qaeda attack was likely to continue.

Then, on August 6, President George W. Bush received a briefing titled “Bin Ladin Determined to Strike in US.”

5:45am: Atta Begins the Final Journey

On the morning of September 11, Mohamed Atta and Abdul Aziz al-Omari flew from Portland to Boston.

Five hijackers boarded American Airlines Flight 77 at Dulles, while four boarded United Airlines Flight 93 at Newark.

By around 8am, all four hijacking teams were in position. The 9/11 Commission later found that the attackers had successfully passed through the aviation-security system in place at the time.

Flight 11 Is Hijacked

American Airlines Flight 11 departed Boston for Los Angeles at 7:59am.

Around 8:14am, the crew stopped responding to air traffic control. The 9/11 Commission believes the hijacking began around that time.

Flight attendants Betty Ong and Amy Sweeney contacted ground personnel and reported that passengers and crew had been stabbed, the cockpit was inaccessible and the attackers had used a substance resembling mace or pepper spray. The hijackers also claimed to have a bomb.

One of the hijackers accidentally transmitted the message, “Nobody move. Everything will be okay,” over the air-traffic-control channel, apparently unaware that controllers could hear the transmission.

8:46am: First World Trade Center Tower Hit

At 8:46am, American Airlines Flight 11 crashed into the North Tower of the World Trade Center.

The Boeing 767 was carrying a large amount of jet fuel. The impact damaged multiple floors, structural columns and fireproofing, but the tower remained standing initially.

The National Institute of Standards and Technology later concluded that the resulting fires weakened exposed steel and, combined with the structural damage, eventually led to the tower’s collapse.

8:42am: Flight 93 Takes Off Late

United Airlines Flight 93 departed Newark at 8:42am, more than 25 minutes behind its scheduled 8am departure.

That delay would become critical.

The hijackers had planned the attacks around departures between roughly 7:45am and 8:10am. Because Flight 93 took off later, passengers had more time to learn about the World Trade Center attacks and understand what was happening aboard their own aircraft.

9:03am: Second Plane Hits the World Trade Center

At 9:03am, United Airlines Flight 175 crashed into the South Tower.

The impact was broadcast live as television networks were already covering the burning North Tower, giving the world its first real-time view of the second attack.

9:28am: Flight 93 Is Hijacked

United Flight 93 was hijacked at approximately 9:28am over eastern Ohio. The struggle in the cockpit was accidentally transmitted to air-traffic controllers.

The pilot or first officer could be heard shouting at the attackers to get out.

Passengers soon began making calls to people on the ground. The 9/11 Commission found that at least 10 passengers and two crew members communicated crucial information to people outside the plane.

At 9:57am, passengers launched their counterattack.

They collectively decided to storm the cockpit. Hijacker-pilot Ziad Jarrah responded by violently rolling and pitching the aircraft in an attempt to prevent them from reaching the controls.

At 10:02am, the plane entered a steep descent.

At 10:03:11am, Flight 93 crashed near Shanksville, Pennsylvania.

The 9/11 Commission concluded that the intended target was probably either the US Capitol or the White House. The passengers’ actions prevented the aircraft from reaching Washington.

9:37am: Pentagon Is Hit

American Airlines Flight 77 was hijacked between approximately 8:51am and 8:54am. Its transponder was switched off, causing it to disappear from conventional radar.

At 9:32am, air-traffic controllers detected the aircraft on primary radar. At about 9:34am, it was roughly 10 kilometres from the Pentagon when it turned and rapidly descended.

At 9:37am, Flight 77 crashed into the Pentagon at roughly 900 kmph.

All 64 people aboard were killed, along with 125 people inside the Pentagon. The US Department of Defense puts the total Pentagon death toll at 189.

9:59am: South Tower Collapses

The South Tower, which had been struck second, collapsed first at 9:59am, after burning for less than an hour.

Hundreds of people inside the building were killed, including firefighters and police officers who had climbed the tower to rescue others.

10:28am: North Tower Collapses

The North Tower collapsed at approximately 10:28am.

NIST estimated that about 87% of the roughly 17,400 people believed to have been inside the two towers successfully evacuated.

NIST found that 619 people in or above the South Tower’s impact zone died.

What Happened to World Trade Center 7?

World Trade Center 7 remains at the centre of persistent conspiracy theories surrounding the attacks.

The 47-storey building, located near the main World Trade Center complex, was not struck by an aircraft. It collapsed at approximately 5:20pm.

NIST concluded that debris from the North Tower damaged WTC 7 and ignited fires on several floors. The building’s sprinkler water supply had also failed, allowing the fires to burn for hours.

Heat caused steel floor beams and girders to expand, eventually contributing to the failure of a critical structural column and triggering a progressive collapse.

NIST also investigated claims that WTC 7 had been destroyed through controlled demolition. It found no evidence of explosives or a missile strike involving WTC 7 or the Twin Towers.

‘America Is Under Attack’

President George W. Bush was in Florida when the attacks began.

At 9:05am, his chief of staff, Andrew Card, entered the classroom where Bush was sitting with children and quietly told him that a second plane had struck the World Trade Center.

Card told the president: “America is under attack.”

The moment was captured in a photograph that became one of the defining images of 9/11.

Osama bin Laden Was Found Nearly a Decade Later

Osama bin Laden remained at large for almost a decade after the attacks.

US intelligence agencies gradually traced his network and identified one of his couriers. By 2010, investigators had linked the courier to a compound in Abbottabad, Pakistan.

On May 2, 2011, US special operations forces raided the compound and killed bin Laden.