In pics | A look back at the scenes from the 9/11 attacks

As the US prepares to mark the 20th anniversary of the 9/11 attacks, a look back at the horrific scenes that transpired after the fall of the World Trade Center Towers in New York City on September 11, 2001, during the terrorist attacks coordinated by al Qaeda, which killed 2,753 people

In this file photo taken on September 11, 2001, smoke billows after the first of the two towers of the World Trade Center collapses

(FILES) In this file photo taken on September 11, 2001, the twin towers of World Trade Center burn after two planes crashed into each building in New York.

In this file photo taken on September 11, 2001, a hijacked commercial aircraft approaches the twin towers of the World Trade Center shortly before crashing into the landmark skyscraper in New York

In this file photo taken on September 11, 2001, pedestrians run from the scene as one of the World Trade Center towers collapses in New York City

In this file photo taken on September 12, 2001, US President George W. Bush (C) and US Secretary of Defense Donald Rumsfeld (L) tour the impact area (rear) at the Pentagon where a hijacked airline crashed into the building as part of a coordinated terrorist attack on the US

In this file photo taken on September 11, 2001, an exausted police officer rests on a car covered in dust near the World Trade Center in New York

In this file photo taken on September 11, 2001, pedestrians walk across the Brooklyn Bridge away from the burning World Trade Center towers before their collapse.

In this file photo taken on September 11, 2001, a police officer (R) and others walk in streets covered in debris following the collapse of the twin towers of the World Trade Center in New York

In this file photo taken on September 11, 2001, the rubble of the twin towers of the World Trade Center smoulder following a terrorist attack in lower Manhattan, New York

In this file photo taken on September 11, 2001, a man stands in the rubble, and calls out asking if anyone needs help, after the collapse of the first of the twin towers of the World Trade Center Tower in lower Manhattan, New York. 

This file photo released by the New York City Office of Emergency Management on September 13, 2001, firefighters and Urban Search and Rescue workers battle smoldering fires as they search for survivors at the ruins of the World Trade Center in New York

This file photo released by the New York City Office of Emergency Management on September 16, 2001 shows an aerial view of the site of the collapsed twin towers of the World Trade Center.

In this file photo taken on September 11, 2001, a man helps evacuate a woman through rubble and debris after the collapse of one of the World Trade Center Towers in New York