WASHINGTON - Officials have released chilling new video of the moments before the Washington Navy Yard massacre.

The video comes as the FBI releases a motive for the deadly shooting. It shows government contractor Aaron Alexis preparing to open fire last Monday.

Alexis went on to shoot and kill 12 people, putting Washington on lockdown.

The FBI has also released photos of his guns, one with the phrase "end the torment" etched into it.

Alexis left a note saying he was driven to kill by low-frequency radio waves.