A general view of downtown Oklahoma City as basketball fans gather outside Oklahoma City Arena. The once run-down area has undergone a major transformation over the past 20 years.
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Spectators bow their heads during a moment of silence during a ceremony to commemorate the 20th anniversary of the Oklahoma City bombing at the Oklahoma City National Memorial, on Sunday.
Aid groups are mobilizing relief efforts to help victims of the storm. Here, Candice Lopez, left, and Stephanie Davis help clean debris from Thelma Cox's mobile home near Shawnee, Okla., after it was destroyed Monday.
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Oklahoma City Bombing: The Albert P. Murrah Federal Building shows the devastation caused by a fuel and fertilizer truck bomb on April 19, 1995. The blast killed 168 people and injured more than 500.
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