SHANKSVILLE, Pa. —

Thursday marks 24 years since nearly 3,000 people were killed as 19 al-Qaeda hijackers seized control of four jetliners on Sept. 11, 2001.

Click here to see the program for today's memorial program . Advertisement

Two planes were flown into the World Trade Center, one into the Pentagon and a fourth into a field in Somerset County.

Observations and memorials are being held at 9/11 ceremonies across the United States, including the attack sites in New York, Washington, D.C., and Shanksville, Pennsylvania.

The observance at the Flight 93 National Memorial commemorates the time when passengers and crew members aboard the plane took action to disrupt the hijackers' plans to fly the plane into a federal building in Washington.

Forty passengers and crew members were ki

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