At first, Dorothy Vong assumed it was a drill -- just like all the others at her work.
At the Inland Regional Center, where she's a nurse, the staff works with clients and parents of clients who are sometimes angry. They have active-shooter drills every month or so.
"Drill started," she texted her husband, Mark, around 11 a.m.
She walked to a window nearby and filmed a video as law enforcement sprinted toward the building.
"Oh, that is scary," a voice says calmly in the background.
"They're all geared up!" someone else says. "Rifles and everything!"
In the background, someone laughs -- they still didn't know.
Then the reality set in.
She texted her husband again: "Well it's real."
And then a few minutes later, another message: "We're in a locked office."
Mark Vong said he told his wife to stay calm and not to panic.
"They train for this," he said, standing outside a police barricade Wednesday afternoon. "They know it's going to happen."
The shooter or shooters who attacked the center apparently opened fire on a Christmas party being held by county employees, federal law enforcement sources and a witness told the Los Angeles Times.
The shooting, which left at least 14 injured and at least 14 dead, happened on the grounds of the Inland Regional Center, which serves people with developmental disabilities in Riverside and San Bernardino counties.
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