SOMBER OCCASION: A memorial service is held on September 11 at Ground Zero, the site of the destroyed World Trade Center twin towers, to mark the 10th anniversary of the September 11 attacks in 2001 (CHEN WEN)

STAR SPANGLED BANNER: The Brooklyn Youth Chorus performs the American national anthem at a ceremony marking the 10th anniversary of the September 11 attacks at Ground Zero in New York City on September 11 (CHEN WEN)

PRESIDENTIAL SPEECH: U.S. President Barack Obama speaks during a ceremony marking the 10th anniversary of the September 11 attacks at Ground Zero in New York City on September 11 (CHEN WEN)

GROUND ZERO REVISITED: Former U.S. President George W. Bush speaks during a ceremony marking the 10th anniversary of the September 11 attacks at Ground Zero in New York City on September 11 (CHEN WEN)

GATHERING CROWD: People gather for a commemoration at Ground Zero in New York City on September 11 (CHEN WEN)

MOMENT OF SILENCE: People mourn in silence at 9:03 a.m., when United Airlines Flight 175 struck the south tower of the World Trade Center 10 years ago (CHEN WEN)

FOR THE BELOVED: Families of the victims read names during a ceremony marking the 10th anniversary of the September 11 attacks at Ground Zero in New York City on September 11 (CHEN WEN)

EXPRESSING SENTIMENTS: Families of the victims hold portraits during a ceremony marking the 10th anniversary of the September 11 attacks at Ground Zero in New York City on September 11 (CHEN WEN)

THROUGH THE DARKNESS: The Tribute in Light rises above the former World Trade Center site in New York City on September 11 (CHEN WEN)

(Reporting from New York)