Largest FBI investigation

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Aerial view of 9/11 Memorial park, Manhattan, New York City.
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.
FBI’s largest crime scenes

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Photo: FBI|Twitter
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.
The crash sites were the largest crime scenes in FBI history and the case included over half-a-million investigative leads, counting several hundred thousand tips from the public.
Remembrance

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Inside 9/11 Memorial & Museum. Photo: Shutterstock
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.
Several other memorials including the Flight 93 National Memorial in a field in Stonycreek Township in Pennsylvania and the Pentagon Memorial in Arlington County in Virginia have been built to remember the victims of September 11 attacks.
Enduring mysteries

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Firefighters walk near the area known as Ground Zero after the collapse of the Twin Towers on September 11, 2001 in New York City. Photo: Shutterstock
The ultimate target of Flight 93 remains one of the biggest mysteries of 9/11.
The authoritative 9/11 Commission report notes that the hijackers had turned the navigation to guide the Boeing 757 towards Washington. But the report is inconclusive about the final destination: The objective of Ziad Jarrah, the pilot among the hijackers, “was to crash his airliner into symbols of the American Republic, the Capitol or the White House.”
The clean-up

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Photo: FBI|Twitter
The clean-up of the World Trade Center site was completed in 2002 while the Pentagon building was repaired within a year.
Global approach towards terrorism

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A visitor stops to reflect at the North Pool of the 9/11 Memorial. Photo: 9/11 Memorial|Twitter
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.
However, post the tragedy, global approach and strategy towards tackling terrorism and its perpetrators were not just changed but revamped.