Today marks the 19th anniversary of the 9/11 terror attack in which nearly 3,000 people were killed in New York, a tragedy that shook the United States and had a huge impact globally. Also Read - Only Trump Can Save America From Another 9/11 Attack, Says Osama Bin Laden's Niece

Also called the September 11 attacks, the attack on New York’s iconic World Trade Centre was a series of four coordinated suicide attacks by the terrorist group al-Qaeda.

On its 19th  anniversary, the 9/11 Memorial & Museum said on Twitter, “Nineteen years ago, under clear blue skies, 102 minutes changed our lives forever. On Fri., Sept. 11, we lead the nation and the world in observing the 19th anniversary of the 2001 attacks and ask you to join us in commemorating.”

Here are some of the lesser-known facts about the September 11 attack:

-The investigation into the 9/11 attacks, code-named “PENTTBOM” was the FBI’s largest investigation ever.

-The crash sites were the largest crime scenes in FBI history and the case included over half-a-million investigative leads.

-Only 20 people were able to survive the crash of the World Trade Center crash.

-The last fires at Ground Zero weren’t extinguished completely until December 19, 2001 and rescue and recovery clean-up of the 1.8 million tons of wreckage from the WTC site took 9 months.

-An estimated 410,000 people were exposed to asbestos, a toxic substance, at WTC in 9/11.

-Over 185,101 tons of steel left at Ground Zero was used in memorials across the US, but some was also sold to China and India.

-The WTC was targeted before as well on February 26, 1993 when a bomb planted in a van parked in the WTC’s underground parking killed six people and wounded more than 1,000.