Danielle Booker hugs her mother, Sharon Booker, as the two remember Sean Booker, Danielle's father and Sharon's husband, at the National September 11 Memorial & Museum during a ceremony on Saturday in Manhattan. Sean Booker was a technician on the 93rd floor of the World Trade Center's north tower when he was killed during the 2001 attacks. RJ Sangosti/MediaNews Group/Denver Post via Getty Images hide caption
Members of the Berlin city fire department attend a ceremony Saturday near the Breitscheidplatz memorial to commemorate fellow firefighters and other victims killed in the 9/11 terror attacks in New York City. Omer Messinger/Getty Images hide caption
Family members and loved ones of victims of those who died on 9/11 attend the 20th anniversary commemoration ceremony on Saturday at the National September 11 Memorial & Museum in New York City. Chip Somodevilla/Pool/AFP/Getty Images hide caption
Ali Malik is part of a class action lawsuit against the FBI alleging religious discrimination and violations of surveillance laws. Umara Chaudry hide caption
In the years after the 9/11 terror attacks, security became omnipresent in Washington, D.C. That includes bollards, Jersey barriers and security barricades like those seen here outside of the U.S. Capitol. Samuel Corum/Getty Images hide caption
Recovery workers head to ground zero in New York City after the Sept. 11, 2001, attacks. Langevin Jacques/Sygma via Getty Images hide caption
President George W. Bush stands in the rubble of the World Trade Center in New York and speaks to workers involved in the cleanup effort on Sept. 14, 2001. Doug Mills/AP hide caption
Teresa Garcia says she remains haunted by the dozens of undocumented workers she believes remain missing at the site of 9/11. Jasmine Garsd/NPR/Jasmine Garsd/NPR hide caption
President Joe Biden speaks about his strategy to combat the coronavirus pandemic at Brookland Middle School on Friday in Washington, D.C. Later in the day, he issued a video commemorating the 20th anniversary of the Sept. 11 terrorist attacks. Manuel Balce Ceneta/AP hide caption
Kiefer Sutherland as Jack Bauer in the 2014 TV show 24: Live Another Day. FOX/FOX Image Collection via Getty I hide caption
An American flag at ground zero on the evening of Sept. 11, 2001, after the terrorist attacks on the World Trade Center in New York City. Mark Lennihan/AP hide caption
Jack Grandcolas, who lost his pregnant wife on United Flight 93, sits near his home in Pebble Beach, Calif. Twenty years after Sept. 11, he is still working through his loss. Haven Daley/AP hide caption
A visitor touches a victim's name inscribed on a bronze parapet at the National September 11 Memorial & Museum in New York City in 2020. Wang Ying/Xinhua News Agency/Getty Images hide caption
These three books provide a detailed accounting of events that have largely defined the U.S. role in the world in the first part of the 21st century. Emily Bogle/NPR hide caption
A man in New York City lights a candle on Sept. 14, 2001, for the victims of the Sept. 11 terrorist attacks. Robert F. Bukaty/AP hide caption