Relatives of victims look at the 9/11 Memorial in New York City, on September 11, 2022, on the 21st anniversary of the attacks on the World Trade Center, Pentagon, and Shanksville, Pennsylvania.

Colonel Davis looks at a photorgaph of her colleague, Captain Micheal Dermott Mullan, at the 9/11 Memorial in New York City, on September 11, 2022, on the 21st anniversary of the attacks on the World Trade Center, Pentagon, and Shanksville, Pennsylvania

Visitors look at US flags displayed on the 9/11 Memorial in New York City, on September 11, 2022, on the 21st anniversary of the attacks on the World Trade Center, Pentagon, and Shanksville, Pennsylvania.

People embrace at the 9/11 Memorial in New York City, on September 11, 2022, on the 21st anniversary of the attacks on the World Trade Center, Pentagon, and Shanksville, Pennsylvania.

A firefighter looks out at the 9/11 Memorial in New York City, on September 11, 2022, on the 21st anniversary of the attacks on the World Trade Center, Pentagon, and Shanksville, Pennsylvania.

An Honor Guard made up of Conroe police and fire personnel present the colors during a September 11th Observance ceremony on the 21st anniversary of the 9/11 attacks, held at the Montgomery County Veterans Memorial Park Sunday, Sept. 11, 2022, in Conroe, Texas.

Attendees salute the flag during a September 11th Observance ceremony on the 21st anniversary of the 9/11 attacks, held at the Montgomery County Veterans Memorial Park Sunday, Sept. 11, 2022 in Conroe, Texas.

A relative of a person who died during the 9/11 terrorist attacks on September 11, 2001, mourns during a remembrance ceremony at the Pentagon in Washington, DC, on September 11, 2022.

A person looks out at the National 9/11 Pentagon Memorial prior to a remembrance ceremony to mark the 21st anniversary of the 9/11 attacks, at the Pentagon in Washington, DC, on September 11, 2022

US President Joe Biden speaks during a remembrance ceremony to mark the 21st anniversary of the 9/11 attacks, at the Pentagon in Washington, DC, on September 11, 2022.

U.S. President Joe Biden delivers remarks at a ceremony commemorating the 21st anniversary of the crash of American Airlines Flight 77 into the Pentagon during the September 11th terrorist attacks at the National 9/11 Pentagon Memorial on September 11, 2022 in Arlington, Virginia. The nation is marking the twenty-first anniversary of the terror attacks of September 11, 2001,

The family of the victims of the 9/11 terror attack listen as their names are read during the annual 9/11 Commemoration Ceremony at the National 9/11 Memorial and Museum on September 11, 2022 in New York City.

Firefighters stand in line during a moment of silence near the 9/11 Memorial in New York City, on September 11, 2022, on the 21st anniversary of the attacks on the World Trade Center, Pentagon, and Shanksville, Pennsylvania.