Remembering 9/11: Twenty Years Later

People pause at 9:59 A.M., the moment 20 years ago the south tower of the World Trade Center fell, during a ceremony at the 9/11 Memorial and Museum on September 11, 2021 in New York City. (Photo by Craig Ruttle-Pool/Getty Images)

New York City Commemorates 20th Anniversary Of 9/11 Terror Attacks

Flags and flowers adorn the names of the victims of the attacks of Sept. 11, 2001, during a ceremony at the 9/11 Memorial and Museum on September 11, 2021 in New York City. (Photo by Craig Ruttle-Pool/Getty Images)

New York City Commemorates 20th Anniversary Of 9/11 Terror Attacks

Flags and flowers adorn the names of the victims of the attacks of Sept. 11, 2001, during a ceremony at the 9/11 Memorial and Museum on September 11, 2021 in New York City. (Photo by Craig Ruttle-Pool/Getty Images)

New York City Commemorates 20th Anniversary Of 9/11 Terror Attacks

Flags and flowers adorn the names of the victims of the attacks of Sept. 11, 2001, during a ceremony at the 9/11 Memorial and Museum on September 11, 2021 in New York City. (Photo by Craig Ruttle-Pool/Getty Images)

New York City Commemorates 20th Anniversary Of 9/11 Terror Attacks

Flags and flowers adorn the names of the victims of the attacks of Sept. 11, 2001, during a ceremony at the 9/11 Memorial and Museum on September 11, 2021 in New York City. (Photo by Craig Ruttle-Pool/Getty Images)

New York City Commemorates 20th Anniversary Of 9/11 Terror Attacks

People view the memorial during a ceremony at the National September 11 Memorial & Museum commemorating the 20th anniversary of the September 11th terrorist attacks on the World Trade Center on September 11, 2021 in New York City. (Photo by Anthony Behar-Pool/Getty Images)

New York City Commemorates 20th Anniversary Of 9/11 Terror Attacks

Firefighters gather in lower Manhattan near Ground Zero as the city commemorates the 20th anniversary of the September 11th terrorist attacks on the World Trade Center on September 11, 2021 in New York City. (Photo by Spencer Platt/Getty Images)

New York City Commemorates 20th Anniversary Of 9/11 Terror Attacks

People attend the annual 9/11 Commemoration Ceremony at the National 9/11 Memorial and Museum on September 11, 2021 in New York City. (Photo by Michael M. Santiago/Getty Images)

New York City Commemorates 20th Anniversary Of 9/11 Terror Attacks

People attend the annual 9/11 Commemoration Ceremony at the National 9/11 Memorial and Museum on September 11, 2021 in New York City. (Photo by Michael M. Santiago/Getty Images)

New York City Commemorates 20th Anniversary Of 9/11 Terror Attacks

Priscella Davis, daughter of fallen Port Authority Police Officer Clinton Davis Sr., holds her son Jaxson, 4, as they view his name during the annual 9/11 Commemoration Ceremony at the National 9/11 Memorial and Museum on September 11, 2021 in New York City. (Photo by Michael M. Santiago/Getty Images)

New York City Commemorates 20th Anniversary Of 9/11 Terror Attacks

Family, friends and colleagues of those killed in the 9/11 and the 1993 bombing terror attacks participate in the annual commemoration ceremony at the National 9/11 Memorial and Museum on September 11, 2021 in New York City. (Photo by Chip Somodevilla/Getty Images)

New York City Commemorates 20th Anniversary Of 9/11 Terror Attacks

Members of the 9/11 Honor Guard salute at the end of their duty at the National 9/11 Memorial at the conclusion of the commemoration ceremony at the memorial on September 11, 2021 in New York City. (Photo by Chip Somodevilla/Getty Images)

9/11: Twenty Years Later

People observe a moment of silence during a ceremony at the National September 11 Memorial & Museum commemorating the 20th anniversary of the September 11th terrorist attacks on the World Trade Center on September 11, 2021 in New York City. (Photo by Mike Segar-Pool/Getty Images)

9/11: Twenty Years Later

People embrace during a ceremony at the National September 11 Memorial & Museum commemorating the 20th anniversary of the September 11th terrorist attacks on the World Trade Center on September 11, 2021 in New York City. (Photo by Mike Segar-Pool/Getty Images)

9/11: Twenty Years Later

A couple embraces near ceremonies for the 20th anniversary of the 9/11 attacks on the World Trade Center near the 9/11 Memorial & Museum in New York, on September 11, 2021. (Photo by ROBERTO SCHMIDT/AFP via Getty Images)

9/11: Twenty Years Later

Members of the NYPD carry a frayed American Flag during a ceremony at the National September 11 Memorial & Museum commemorating the 20th anniversary of the September 11th terrorist attacks on the World Trade Center on September 11, 2021 in New York City. (Photo by Anthony Behar-Pool/Getty Images)

9/11: Twenty Years Later

A crowd forms near Freedom Tower as they participate in the 20th anniversary of the 9/11 attacks on the World Trade Center near the 9/11 Memorial & Museum in New York, on September 11, 2021. (Photo by ROBERTO SCHMIDT/AFP via Getty Images)

9/11: Twenty Years Later

A couple embrace near ceremonies for the 20th anniversary of the 9/11 attacks on the World Trade Center near the 9/11 Memorial & Museum in New York, on September 11, 2021. (Photo by ROBERTO SCHMIDT/AFP via Getty Images)

9/11: Twenty Years Later

Former President Barack Obama, former First Lady Michelle Obama, President Joe Biden, First Lady Jill Biden and former New York City Mayor Michael Bloomberg attend the annual 9/11 Commemoration Ceremony at the National 9/11 Memorial and Museum on September 11, 2021 in New York. (Photo by CHIP SOMODEVILLA/POOL/AFP via Getty Images)

New York City Commemorates 20th Anniversary Of 9/11 Terror Attacks

U.S. Attorney General Merrick Garland visits the National 9/11 Memorial during the commemoration ceremony at the memorial on September 11, 2021 in New York City. (Photo by Chip Somodevilla/Getty Images)

9/11: Twenty Years Later

Firefighters take part in a moment of silence on the 20th anniversary of the 9/11 attacks on the World Trade Center in New York, on September 11, 2021.(Photo by ANGELA WEISS/AFP via Getty Images)

9/11: Twenty Years Later

Firefighters walk through a street in the Brooklyn borough of New York on the 20th anniversary of the 9/11 attacks on the World Trade Center in New York, on September 11, 2021. (Photo by ANGELA WEISS/AFP via Getty Images)

9/11: Twenty Years Later

A bell is rung during a moment of silence during the annual 9/11 Commemoration Ceremony at the National 9/11 Memorial and Museum on September 11, 2021 in New York. (Photo by Chip Somodevilla / POOL /AFP via Getty Images)

9/11: Twenty Years Later

A woman closes her eyes near ceremonies for the 20th anniversary of the 9/11 attacks on the World Trade Center near the 9/11 Memorial & Museum in New York, on September 11, 2021. (Photo by ROBERTO SCHMIDT/AFP via Getty Images)

9/11: Twenty Years Later

Firefighters take part in a moment of silence on the 20th anniversary of the 9/11 attacks on the World Trade Center in New York, on September 11, 2021. (Photo by ANGELA WEISS/AFP via Getty Images)

9/11: Twenty Years Later

Firefighters and others take part in a moment of silence on the 20th anniversary of the 9/11 attacks on the World Trade Center in New York, on September 11, 2021. (Photo by ANGELA WEISS/AFP via Getty Images)

9/11: Twenty Years Later

Joe Walker, a man who lives in the neighborhood, wipes a tear from his face as he participates in the 20th anniversary of the 9/11 attacks on the World Trade Center near the 9/11 Memorial & Museum in New York, on September 11, 2021. (Photo by ROBERTO SCHMIDT/AFP via Getty Images)

9/11: Twenty Years Later

Flowers are seen on the 9/11 Memorial during a ceremony at the National September 11 Memorial & Museum commemorating the 20th anniversary of the September 11th terrorist attacks on the World Trade Center on September 11, 2021 in New York City. (Photo by Mike Segar-Pool/Getty Images)

9/11: Twenty Years Later

Four sisters make a charcoal imprint of the name of their cousin Richard Avery Aronow during a ceremony at the National September 11 Memorial & Museum commemorating the 20th anniversary of the September 11th terrorist attacks on the World Trade Center on September 11, 2021 in New York City. (Photo by Anthony Behar-Pool/Getty Images)

9/11: Twenty Years Later

Joe Walker, a man who lives in the neighborhood, wipes a tear from his face as he participates in the 20th anniversary of the 9/11 attacks on the World Trade Center near the 9/11 Memorial & Museum in New York, on September 11, 2021. (Photo by ROBERTO SCHMIDT/AFP via Getty Images)

9/11: Twenty Years Later

Katie Mascali is comforted by her fiance Andre Jabban as they stand near the name of her father Joseph Mascali during a ceremony at the National September 11 Memorial & Museum on September 11, 2021 in New York City. (Photo by Craig Ruttle - Pool/Getty Images)

9/11: Twenty Years Later

Mary Ellen Davis shields the sun from her eyes as she participates in the 20th anniversary of the 9/11 attacks on the World Trade Center near the 9/11 Memorial & Museum in New York, on September 11, 2021. (Photo by ROBERTO SCHMIDT / AFP via Getty Images)

9/11: Twenty Years Later

Firefighters from FDNY Engine Company 217, Brooklyn, salute near the name of their fallen colleagues during the 20th anniversary Memorial at the World Trade Center on September 11, 2021 in New York. (Photo by David Handschuh / POOL / AFP via Getty Images)

9/11: Twenty Years Later

Randall Goosby (R) and pianist Zhu Wang perform during the annual 9/11 Commemoration Ceremony at the National 9/11 Memorial and Museum on September 11, 2021 in New York. (Photo by Chip Somodevilla / POOL / Getty Images)

9/11: Twenty Years Later

Family members and loved ones of victims attend the annual 9/11 Commemoration Ceremony at the National 9/11 Memorial and Museum on September 11, 2021 in New York. (Photo by David Handschuh / POOL / Getty Images)

9/11: Twenty Years Later

Bruce Springsteen performs during the annual 9/11 Commemoration Ceremony at the National 9/11 Memorial and Museum on September 11, 2021 in New York City. (Photo by Chip Somodevilla/Getty Images)

9/11: Twenty Years Later

NYPD and FDNY Memorial Ceremony at FDNY Engine 8, Ladder 2, Battalion 8 on September 11, 2021 in New York City. (Photo by Kevin Mazur/Getty Images)

9/11: Twenty Years Later

A bell is rung during a moment of silence during the annual 9/11 Commemoration Ceremony at the National 9/11 Memorial and Museum on September 11, 2021 in New York City. (Photo by Chip Somodevilla/Getty Images)