Former Massey Energy Company Chairman and CEO Don Blankenship, seen in July 2010, has pleaded not guilty to conspiracy charges associated with the 2010 West Virginia mine explosion that killed 29 men. Jacquelyn Martin/AP hide caption

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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. Bob Daemmrich/AFP/Getty Images hide caption

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Mine helmets and painted crosses sat at the entrance to Massey Energy's Upper Big Branch coal mine on April 5, as a memorial to the 29 miners killed there one year earlier. Jeff Gentner/AP hide caption

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Mine Safety Agency Reports Failures Before Deadly Explosion

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