9/11, 20 years later

A survivor sits outside the World Trade Center after two planes hit the building September 11, 2001 in New York City. (Photo by Jose Jimenez/Primera Hora/Getty Images)

A man holds a picture of a missing woman as he searches for information about her following the attack on the World Trade Center in New York, New York, USA on 14 September 2001 (reissued 03 September 2021). EPA-EFE/TANNEN MAURY

A woman reads a copy of an evening newspaper reporting the terrorist attacks on the United States on an underground train September 11, 2001 in London. (Photo by Graham Barclay/BWP Media/Getty Images)

U.S. President George W. Bush sits at his desk in the Oval Office after addressing the nation about the terrorist attacks on New York and Washington, DC September 11, 2001 in Washington, DC. (Photo by Mark Wilson/Getty Images)

Smoke pours from the twin towers of the World Trade Center after they were hit by two hijacked airliners in a terrorist attack September 11, 2001 in New York City. (Photo by Robert Giroux/Getty Images)

People run away as the North Tower of World Trade Center collapses after a hijacked airliner hit the building September 11, 2001 in New York City. (Photo by Jose Jimenez/Primera Hora/Getty Images)

Policemen and firemen run away from the huge dust cloud caused as the World Trade Center's Tower One collapses after terrorists crashed two hijacked planes into the twin towers, September 11, 2001 in New York City. (Photo by Jose Jimenez/Primera Hora/Getty Images)

People walk in the street in the area where the World Trade Center buildings collapsed September 11, 2001 after two airplanes slammed into the twin towers in a suspected terrorist attack. (Photo by Mario Tama/Getty Images)

Firefighters walk towards one of the tower at the World Trade Center before it collapsed after a plane hit the building September 11, 2001 in New York City. (Photo by Jose Jimenez/Primera Hora/Getty Images)

People hang from the windows of the North Tower of the World Trade Center after a hijacked airliner hit the building September 11, 2001 in New York City. (Photo by Jose Jimenez/Primera Hora/Getty Images)

This is a view from West Broadway Avenue of the downtown Manhattan area of the World Trade Center towers after they were hit by two planes during a terrorist attack September 11, 2001 in New York City. (Jose Jimenez/Primera Hora via Getty Images)

People walk over the Brooklyn Bridge as the world trade center burns September 11, 2001 after two hijacked airplanes slammed into the twin towers in New York City. (Photo by Spencer Platt/Getty Images)

Rescue workers search the still-smoldering debris of the destroyed World Trade Center in New York, New York, USA, 19 September 2001 (reissued 03 September 2021). EPA-EFE/ANJA NIEDRINGHAUS

An unidentified New York City firefighter walks away from Ground Zero after the collapse of the Twin Towers September 11, 2001 in New York City. The World Trade Center's Twin Towers and the Pentagon were attacked by terrorists using commercial airliners as missiles. (Photo by Anthony Correia/Getty Images)

An unidentified New York City firefighter walks away from Ground Zero after the collapse of the Twin Towers September 11, 2001 in New York City. The World Trade Center's Twin Towers and the Pentagon were attacked by terrorists using commercial airliners as missiles. (Photo by Anthony Correia/Getty Images)

The moon rises over the destroyed remains of the World Trade Center in New York, New York, USA as seen from Liberty State Park in Liberty City, New Jersey, USA, on the morning of 12 September 2001 (reissued 03 September 2021). EPA-EFE/TANNEN MAURY

Smoke continues to rise from the destroyed World Trade Center in New York, USA, 15 September 2001 (reissued 03 September 2021).  EPA-EFE/KEITH MEYERS / POOL

A dust-covered bronze statue of a man with his briefcase rests in the rubble of the World Trade Center in New York, USA, 13 September 2001 (reissued 03 September 2021).  EPA-EFE/BETH A. KEISER / POOL

A pedestrian walks to the South Bridge of the World Financial Center August 27, 2002 in New York City. (Photo by Mario Tama/Getty Images)

Ash and soot cover the World Financial Center September 14, 2001 in New York's financial district. (Photo by Jim Watson/US Navy/Getty Images)

Fires still burn amidst the rubble of the World Trade Center September 13, 2001 days after the September 11, 2001 terrorist attack. (U.S. Navy Photo by Jim Watson/Getty Images)

Fire and rescue workers search through the rubble of the World Trade Center in New York, USA, 13 September 2001 (reissued 03 September 2021). EPA-EFE/BETH A. KEISER / POOL

A military helicopter flies in front of the Pentagon September 14, 2001 in Arlington, Virginia at the impact site where a hijacked airliner crashed into the building. (Photo by Stephen J. Boitano/Getty Images)

A woman mourns September 13, 2001 in the Franklin D. Roosevelt Garden near the U.S. Embassy in London, where floral tributes were laid after the terrorist attacks in the U.S. (Photo by Sion Touhig/Getty Images)

The daughter of police officer Moira Smith who was killed on 9-11, Patricia Smith, holds the hand of her father James Smith on stage during the reading of names of victims of 9-11 during ceremonies at Ground Zero September 11, 2006 in New York City. (Photo by Spencer Platt/Getty Images)

Robert Peraza, who lost his son Robert David Peraza, pauses at his son's name at the North Pool of the 9/11 Memorial during tenth-anniversary ceremonies at the site of the World Trade Center in New York, New York, USA, 11 September 2011. EPA-EFE/JUSTIN LANE

U.S. President George W. Bush holds an American flag during a Memorial Service at the Pentagon October 11, 2001 in Arlington, Virginia. (Photo by Mark Wilson/Getty Images)

American flags fly at half staff on the grounds of the Washington Monument in memory of the victims of the terror attacks in New York City and at the Pentagon September 17, 2001 in Washington, DC. (Photo by Alex Wong/Getty Images)

As the sun sets over New Jersey, cleanup and recovery efforts continue at the site of the World Trade Center disaster February 15, 2002 in New York City. (Photo by Spencer Platt/Getty Images)

People cheer on rescue workers on the West Side Drive September 13, 2001 in New York City after the destruction of the World Trade Center, which killed some 3,000 people. (Photo by Spencer Platt/Getty Images)

September 11th missing person posters are shown attached to a wall outside Saint Vincent's Hospital August 22, 2002 in New York City.  (Photo by Mario Tama/Getty Images)

A woman looks at pictures and messages searching for missing people on a wall in Manhattan, New York, USA, 21 September 2001 as rescue workers are still searching for more than 6,000 people in the debris of the World Trade Center (reissued 03 September 2021). EPA-EFE/ANJA NIEDRINGHAUS

Firefighters stand atop a fire engine with the flag-draped casket of fellow fireman Lt. Dennis Mojica September 21, 2001 during a funeral service at St. Patrick's Cathedral in New York City.  (Photo by Joe Raedle/Gettyimages)

In this handout image provided by The White House, President Barack Obama, Vice President Joe Biden, Secretary of State Hillary Clinton and members of the national security team receive an update on the mission against Osama bin Laden in the Situation Room of the White House May 1, 2011 in Washington, DC. Obama later announced that the United States had killed Bin Laden in an operation led by U.S. Special Forces at a compound in Abbottabad, Pakistan. (Photo by Pete Souza/The White House via Getty Images)

Pakistanis along with international and local media gather outside Osama Bin Laden's compound, where he was killed during a raid by U.S. special forces, May 3, 2011 in Abottabad, Pakistan. Bin Laden was killed during a U.S. military mission May 2, at the compound. According to reports May 4, 2011, the Obama administration has decided not to release photographs of Bin Laden's body. (Photo by Getty Images)

U.S. President Barack Obama departs after making a televised statement at the White House in Washington, D.C., U.S., on Monday, May 1, 2011. Al-Qaeda leader Osama bin Laden has been killed in a U.S. operation, Obama said. Photographer: Brendan Smialowski/Pool via Bloomberg

A man holds up a scoreboard on his ipad displaying Obama - one, Osama - nil, as thousands of people celebrate in the streets at Ground Zero, the site of the World Trade Centre, waving American flags and honking horns to celebrate the death of al Qaeda founder and leader Osama bin Laden on May 1, 2011 in New York City. (Photo by Spencer Platt/Getty Images)

Cleaners prepare the Empty Sky Memorial, a monument honouring New Jerseys' 9/11 victims, ahead of the 20th anniversary of 9/11 in Jersey City, New Jersey, USA, 08 September 2021. The 20th anniversary of the worst terrorist attack on US soil will be observed on 11 September 2021. EPA-EFE/WILL OLIVER

The "Tribute in Light" memorial to the World Trade Center is seen from the Empire State Building April 3, 2002 in New York City. (Photo by Mario Tama/Getty Images)

People walk past the 9/11 Memorial in Weehawken, opposite Manhattan Island, New York, USA, 09 September 2021. The 20th anniversary of the worst terrorist attack on US soil will be observed on 11 September 2021. EPA-EFE/WILL OLIVER

A volunteer places an American flag as part of a display to commemorate the victims of the 11 September 2001 attacks on US soil, at the Pepperdine University in Malibu, California, USA, 08 September 2021. EPA-EFE/ETIENNE LAURENT DM/ ML