Aaron Alexis, shown in a handout photo
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Navy Yard gunman Aaron Alexis had valid access pass

17 September 2013 Last updated at 16:42 BST

Aaron Alexis, who killed 12 people at the Washington Navy Yard on Monday, had a valid pass to access the secure building, the BBC's Rajini Vaidyanathan reports.

Meanwhile, investigators have yet to discover a motive for the shooting.