No evidence of wrongdoing but odd statements from mother in hot car death raises suspicion. David Mattingly reports.
The U.S. averages one school shooting every five weeks since the killings in Newtown. CNN's David Mattingly reports.
At the height of the Cold War, a secret underground bunker was built to keep U.S. leaders safe. David Mattingly reports.
CNN's David Mattingly looks at how the Tsarnaev brothers built the explosives they used in the Boston Marathon bombings.
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