A striking video recorded inside a San Bernardino, California, social services center shortly after at least 14 people were gunned down shows the dramatic moment when police swarmed the building.
The 30-second clip, obtained by the Los Angeles Times, was taken by nurse Dorothy Vong around 11 a.m. on Wednesday. Vong and several unseen colleagues initially thought the officers were part of an active-shooter drill, and bouts of laughter can be heard in the background.
The reality quickly sets in as the police are seen rushing toward the Inland Regional Center "all geared up," as one voice says, with "rifles and everything."
The center, which helps individuals with developmental disabilities, has active-shooter drills about every month, the LA Times notes. The frequency reflects the troubling reality that America has seen more mass shootings this year than the number of days that have passed in 2015.
Two shooters, one female and one male, are dead after the San Bernardino attack, which has turned out to be the deadliest massacre in the U.S. since the 2012 shooting at Sandy Hook Elementary School.
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