A list of commemorations planned at 3 crash sites on the 12th anniversary of Sept. 11 attacks

A look at events in New York City, Washington and Shanksville, Pa., marking the 12th anniversary of the Sept. 11 attacks:

NEW YORK CITY

In a sadly familiar ceremony, friends and relatives of World Trade Center attack victims gathered at the National Sept. 11 Memorial plaza to call out the names of the dead and read messages to their lost loved ones.

A bell tolled to mark the moments when four hijacked jets crashed into the twin towers, the Pentagon and a field in the Pennsylvania countryside, and again to mark the moments when the two skyscrapers collapsed.

Several politicians attended, including New Jersey Gov. Chris Christie and former New York Gov. George Pataki, but none gave an address.

WASHINGTON

President Barack Obama held a moment of silence at 8:46 a.m. on the White House's South Lawn to mark the first attack in New York. He was joined by Michelle Obama, Vice President Joe Biden and his wife Jill Biden. A bugler played "Taps."

At the Pentagon Sept. 11 memorial in Arlington, Va., victims' families, attack survivors and military officials laid a wreath and held a moment of silence at 9:37 a.m. to mark the moment that Flight 77 hit the building.

Pentagon employees were to attend a separate event at 1 p.m. in the complex's courtyard.

PENNSYLVANIA

At 10:03 a.m., bells were rung and names of passengers and crew members were read at the Flight 93 National Memorial.