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The iconic Taliban flag is painted on a wall outside the American embassy compound in Kabul, Afghanistan, Saturday, Sept. 11, 2021. (AP Photo / Bernat Armangue)

The Taliban raised their flag over the Afghan presidential palace Saturday, a spokesman said, as the U.S. and the world marked the 20th anniversary of the Sept. 11 attacks.

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An American flag is unfurled at the Pentagon in Washington, Saturday, Sept. 11, 2021, at sunrise on the morning of the 20th anniversary of the terrorist attacks. (AP Photo / Alex Brandon)

The document released Saturday, on the 20th anniversary of the attacks, is the first investigative record to be disclosed since President Joe Biden ordered a declassification review of materials that for years have remained out of public view. 

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(L-R)  former President Bill Clinton, former First Lady Hillary Clinton, former President Barack Obama, former First Lady Michelle Obama, President Joe Biden, First Lady Jill Biden, former New York City Mayor Michael Bloomberg, Bloomberg's partner Diana Taylor, Speaker of the House Nancy Pelosi and Senate Minority Leader Charles Schumer stand for the national anthem during the annual 9/11 Commemoration Ceremony at the National 9/11 Memorial and Museum Sept. 11, 2021 in New York. (Chip Somodevilla / AP)

Presidents Joe Biden, Barack Obama and Bill Clinton all gathered at the site where the World Trade Center towers fell two decades ago. 

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A memorial flag is brought onto the stage during ceremonies to commemorate the 20th anniversary of the Sept. 11 terrorist attacks, Saturday, Sept. 11, 2021, at the National September 11 Memorial & Museum in New York. (AP Photo/John Minchillo)

The ceremony at ground zero in New York began exactly two decades after the deadliest act of terrorism on U.S. soil started with the first of four hijacked planes crashing into one of the World Trade Center’s twin towers.

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President Joe Biden and first lady Jill Biden watch as a carry team moves the transfer case containing the remains of Navy Corpsman Maxton W. Soviak, 22, of Berlin Heights, Ohio, during a casualty return Sunday, Aug. 29, 2021, at Dover Air Force Base, Del. (AP Photo / Carolyn Kaster)

This 9/11 comes little more than two weeks after a suicide bomber in Kabul killed 13 U.S. service members as the military concluded its withdrawal from Afghanistan. 

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In this Sept. 11, 2001 file photo, people covered in dust from the collapsed World Trade Center buildings, walk through the area, in New York. (AP Photo / Suzanne Plunkett, File)

Two decades after the twin towers’ collapse, people are still coming forward to report illnesses that might be related to the attacks. 

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This April 28, 2021, file photo shows the U.S. Capitol building in Washington. (AP Photo / J. Scott Applewhite, File)

Ten years after the 9/11 attacks, Americans were reasonably positive about the state of their rights and liberties. Today, after 20 years, not as much.

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The First Responders Memorial is right on the Oak Lawn Patriot Station Metra stop. The memorial’s spires are partially made with beams from the World Trade Center. (WTTW News)

Oak Lawn is a southwest suburb bordering parts of Chicago. Along with surrounding suburbs, it has a strong Muslim community. And its fire and police departments sent members to support New York firefighters after the 9/11 attack. 

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The terrorist attacks of Sept. 11, 2001 have changed the world in ways both “subtle and profound,” said DePaul University history professor Thomas Mockaitis. (WTTW News)

Saturday marks the 20th anniversary of the deadliest terrorist attack on U.S. soil. Local experts join us to discuss what we’ve learned about terrorist threats since then — and how safe we are today.

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A woman walks by the colorful murals that surround the foundation for 2 World Trade Center, Wednesday, Sept. 8, 2021 in New York. (AP Photo / Mark Lennihan)

Two planned skyscrapers, a performing arts center and a church are still unfinished at the World Trade Center complex, which plays host Saturday to the annual ceremony honoring nearly 3,000 people killed in the attacks.

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Margot Eckert stands by a display of pictures of her brother-in-law Sean Rooney and sister Beverly Eckert at her home, Thursday, July 15, 2021, in Springfield, Mass. (AP Photo / Robert Bumsted)

A collection of some 22,000 personal artifacts — some on display at the 9/11 Memorial & Museum, and others on display at other museums around the country — provide a mosaic of lost lives and stories of survival: wallets, passports, baseball gloves, shoes, clothes and rings.

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Comedian Dave Chappelle arrives at Kennedy Center for the Performing Arts to receive the 22nd Annual Mark Twain Prize for American Humor in Washington on Oct. 27, 2019, left, and comedian Jon Stewart performs at the 9th Annual Stand Up For Heroes event in New York on Nov. 10, 2015. (AP Photo)

A star-studded group of comedians will perform for one night only at Madison Square Garden to mark the 20th anniversary of 9/11.

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President Joe Biden returns a salute as he walks to board Air Force One to travel to Louisiana to view damage caused by Hurricane Ida, Friday, Sept. 3, 2021, in Andrews Air Force Base, Md. (AP Photo / Evan Vucci)

President Joe Biden will visit all three 9/11 memorial sites to commemorate the 20th anniversary of the Sept. 11 attacks and pay his respects to the nearly 3,000 people killed that day. 

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In this Sept. 11, 2017, file photo, the Tribute in Light illuminates in the sky above the Lower Manhattan area of New York, as seen from across the Hudson River in Jersey City, N.J. (AP Photo / Jason DeCrow, File)

In a year when the coronavirus pandemic has reshaped countless American rituals, even the commemoration of 9/11 could not escape unchanged.

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In this May 15, 2015 file photo, visitors gather near the pools at the 9/11 Memorial in New York. As they have done 17 times before, a crowd of victims' relatives is expected at the site on Wednesday, Sept. 11, 2019 to observe the anniversary the deadliest terror attack on American soil. (AP Photo / Frank Franklin II)

Eighteen years after the deadliest terrorist attack on American soil, the nation is still grappling with the aftermath at ground zero, in Congress and beyond. 

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Janet Napolitano (Credit: University of California)

How safe is America from terror attacks and other threats? Former Homeland Security Secretary Janet Napolitano talks about whether the U.S. has gotten safer since the 9/11 terror attacks.