 "19 years of 9/11 attacks: Some lesser known facts")
The investigation into the 9/11 or September 11 attacks was code-named "PENTTBOM" and is the largest FBI investigation to date. More than half of the Federal Bureau of Investigation (FBI) agents were involved at the peak of the case, to identify the hijackers and sponsors of the attack.
The 9/11 tragedy was a series of four coordinated suicide attacks by the terrorist group al-Qaeda, who first hijacked four US passenger planes between 8 and 9 am and crashed them into the the World Trade Center complex in Manhattan, Pentagon in Virginia, and field in Pennsylvania.
Every year, the National September 11 Memorial & Museum conducts a free interactive program on and around the 9/11 anniversary that connects participants with museum staff members and guest speakers to learn about the attacks and the importance of commemoration.
The ultimate target of Flight 93 remains one of the biggest mysteries of 9/11.
The clean-up of the World Trade Center site was completed in 2002 while the Pentagon building was repaired within a year.
September 11 attacks were one of the worst in history, killing nearly 3,000 people. Besides, over 6,000 people were injured in the series of attacks. However, post the tragedy, global approach and strategy towards tackling terrorism and its perpetrators were not just changed but revamped.