Security Tightens at US Capitol

In This Photo: Aaron Alexis
In this handout photo provided by the FBI, Aaron Alexis is shown in a photo prior to the mass shooting at the Washington Navy Yard on September 16, 2013 in Washington, D.C. Authorities believe Alexis was a gunman involved in the shootings at the Navy Yard, where at least 12 people were shot and killed.
(Sept. 15, 2013 - Source: Handout/Getty Images North America) more pics from this album »