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 Members of U. military forces stood next to benches during a cereomy at the National 9/11 Pentagon Memorial  in Arlington, Va.
Members of U. military forces stood next to benches during a cereomy at the National 9/11 Pentagon Memorial in Arlington, Va.(Alex Wong/Getty Images)
Family members of those killed in the 9/11 attacks lay flowers and press pennies into a memorial before a 9/11 wreath laying ceremony at Boston Public Garden.
Family members of those killed in the 9/11 attacks lay flowers and press pennies into a memorial before a 9/11 wreath laying ceremony at Boston Public Garden.(Jessica Rinaldi/Globe Staff)
A man paused at the north pool before the start of a commemoration ceremony for the victims of the September 11 terrorist attacks at the National September 11 Memorial, in New York City.
A man paused at the north pool before the start of a commemoration ceremony for the victims of the September 11 terrorist attacks at the National September 11 Memorial, in New York City. (Drew Angerer/Getty Images)
John Krajovic is hugged by Joni Belfiore inside the Logan Airport 911 Memorial. Krajovic was the Massport Project Director for the memorial, and Belfiore is an employee of Massport.
John Krajovic is hugged by Joni Belfiore inside the Logan Airport 911 Memorial. Krajovic was the Massport Project Director for the memorial, and Belfiore is an employee of Massport. (John Tlumacki/Globe Staff)
A woman left flowers at the North Pool of the 9/11 Memorial in New York.
A woman left flowers at the North Pool of the 9/11 Memorial in New York. (Mark Lennihan/Associated Press)
Bill Anders (left) and Sharon Custer rang bells as part of the Name Presentation and Ringing of Bells Remembrance in Shanksville, Pa.
Bill Anders (left) and Sharon Custer rang bells as part of the Name Presentation and Ringing of Bells Remembrance in Shanksville, Pa.(Gene J. Puskar/Associated Press)
Family members attended the September 11th Flight 93 Memorial Service in Shanksville, Pa.
Family members attended the September 11th Flight 93 Memorial Service in Shanksville, Pa.(Evan Vucci/Associated Press)
The family of Madeline "Amy" Sweeney, the flight attendant on American Flight 11, embraced after the award ceremony honoring her. It is called The Madeline "Amy" Sweeney Award for Civilian Bravery. Her daughter, Anna Sweeney is on the right.
The family of Madeline "Amy" Sweeney, the flight attendant on American Flight 11, embraced after the award ceremony honoring her. It is called The Madeline "Amy" Sweeney Award for Civilian Bravery. Her daughter, Anna Sweeney is on the right. (Suzanne Kreiter/Globe staff)
A flag is unfurled at sunrise at the Pentagon on the 17th anniversary of the September 11th attacks.
A flag is unfurled at sunrise at the Pentagon on the 17th anniversary of the September 11th attacks. (Pablo Martinez Monsivais/Associated Press)
A man wiped a tear while pausing by the South Pool of the 9/11 Memorial in New York.
A man wiped a tear while pausing by the South Pool of the 9/11 Memorial in New York.(JUSTIN LANE/EPA/Shutterstock)
Flowers are seen at the National 9/11 Pentagon Memorial.
Flowers are seen at the National 9/11 Pentagon Memorial. (MICHAEL REYNOLDS/EPA/Shutterstock)
A young boy and his mother looked down into the South Pool in New York.
A young boy and his mother looked down into the South Pool in New York.(TIMOTHY A. CLARY/AFP/Getty Images)
White House Chief of Staff John Kelly (center) placed his hand over his heart during the playing of "Taps" while joining members of the White House staff in observing a moment of silence on the south lawn of the White House.
White House Chief of Staff John Kelly (center) placed his hand over his heart during the playing of "Taps" while joining members of the White House staff in observing a moment of silence on the south lawn of the White House.(Win McNamee/Getty Images)
Flowers are placed on the names of those who perished on the wall around the South Pool in New York.
Flowers are placed on the names of those who perished on the wall around the South Pool in New York.(TIMOTHY A. CLARY/AFP/Getty Images)
President Donald Trump and first lady Melania Trump, escorted by Stephen Clark, Superintendent of the National Parks of Western Pennsylvania, walked along the September 11th Flight 93 memorial in Shanksville, Pa.
President Donald Trump and first lady Melania Trump, escorted by Stephen Clark, Superintendent of the National Parks of Western Pennsylvania, walked along the September 11th Flight 93 memorial in Shanksville, Pa.(Evan Vucci/Associated Press)
 A family member whose loved one was killed in the September 11th attacks lays flowers during a 9/11 wreath laying ceremony at Boston Public Garden.
A family member whose loved one was killed in the September 11th attacks lays flowers during a 9/11 wreath laying ceremony at Boston Public Garden.(Jessica Rinaldi/Globe Staff)
Sailors saluted the Colors, as the National Anthem is played. The USS Constitution held a 9/11 remembrance ceremony, with one-gun salutes marking moments planes hit and towers fell.
Sailors saluted the Colors, as the National Anthem is played. The USS Constitution held a 9/11 remembrance ceremony, with one-gun salutes marking moments planes hit and towers fell. (Pat Greenhouse/Globe Staff)