Paula Silva, a Barnes & Noble employee, said once she realized what was happening, she and her coworkers turned off all the lights and moved customers into the stockroom.
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"We were hiding in the dark, we turned off the lights as soon as we locked the doors."
Silva described people looking scared and shaking as they waited to be escorted out.
"It was pretty scary. Seeing all my co-workers scared caught me off guard."
Listen to her full interview in the video player above.
Watch the video above to hear the full interview.
Get the latest updates on the San Bruno mall shooting here.