As US marks 21 years of 9/11, here are some lesser known facts about the deadly attacks

The September 11 attacks, commonly known as the 9/11 attacks, marked the 21st anniversary on Sunday, with people still mourning the deaths of their loved ones. More than two decades have passed since the deadliest terrorist strike on US soil, but it continues to hound Americans as they remember 9/11 with silent moments, recitation of victims' names, volunteer work, and other tributes. Every year on September 11, the family members of victims and dignitaries in the US gather at the Pentagon, the World Trade Center (WTC) in New York, and a field in Pennsylvania - the three places where hijacked aircraft crashed.  

Here are some lesser-known facts about September 11 attacks:

• Four commercial aircraft were hijacked by 19 terrorists from the Islamist extremist organisation, Al-Qaeda, to launch attacks across the United States. Two of these hijacked aircraft crashed into the World Trade Center's twin towers. 
• The terrorists first crashed into floors 93 and 99 of the WTC's North Tower at around 8:46 AM (local time), whereas, the second aircraft stormed into South Tower around 9:03 AM. Around 18,000 people were present at the WTC complex when the strike took place. 
• The third aircraft struck the Pentagon in Arlington city. The passengers of the fourth hijacked plane retaliated after learning about the other attacks, and the aircraft ultimately crashed into a field in the western part of Pennsylvania. 
• As many as 2,977 people from 93 countries were killed in the attacks.  Of them, 2,753 people were killed in the twin towers attack, while 184 were killed at the Pentagon. The other 40 were killed in the plane which crashed in Pennsylvania.
• Osama bin Laden, the leader of Al-Qaeda, and his allies made the strategy to carry out the 9/11 attacks. One terrorist each from Lebanon and Egypt, two from the United Arab Emirates, and fifteen from Saudi Arabia comprised of 19 terrorists that finally carried out the attacks.
• Following the attack, the US launched a series of operations to destroy bases of al-Qaeda and other such terrorist organisations. Osama bin Laden, the mastermind of the attacks, was finally killed in a military operation carried out by the US agencies at his hideout in Pakistan’s Abbottabad city. 
•  Al-Qaeda leader and another conspirator of the 9/11 attacks, Ayman al-Zawahiri, was killed by the US agency in August this year in Afghanistan. 
• The largest FBI investigation to date is "PENTTBOM," which relates to the inquiry into the 9/11 attacks. At the peak of the investigation, more than half of the FBI's agents were working to track down the attackers and their sponsors.

Image: AP