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Aaron Alexis moves through Navy Yard building with shotgun

Alexis moves through the hallways of building 197 carrying a Remington 870 shotgun. (FBI)

FBI releases chilling images of Navy Yard gunman

Yahoo NewsSeptember 25, 2013

The Federal Bureau of Investigation released footage and still images of Aaron Alexis, the 34-year-old Washington Navy Yard gunman, moving through the building where investigators say he shot and killed 12 people and wounded four others in the Sept. 16, 2013 massacre before he was shot dead by law enforcement.

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