CCTV footage of gunman Aaron Alexis
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Navy Yard shooting: CCTV shows gunman Aaron Alexis

The FBI has released footage of gunman Aaron Alexis who shot dead 12 people at a Navy Yard in Washington.

The 34-year-old is seen stalking the corridors of the complex on 16 September. He was eventually shot by police in a running gun battle.

Valerie Parlave, head of the FBI's field office in Washington, said they were still investigating Alexis' background and motivations.

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