YouTube employee Diana Arnspiger told the Associated Press that she had glimpsed the shooter from a second-floor window.

“We heard ‘boom! boom!’ you know, and looked up and didn’t know what it was, and I ran to the window because the window behind me overlooks the patio, and I saw her,” said Arnspiger.

Another employee, Todd Sherman, tweeted that he spotted drops of blood on the floor on his way out of the building. In videos posted to Snapchat, numerous people were also seen exiting the office building with their hands in the air.

YouTube CEO Susan Wojcicki said she had no words to describe the horror of the day, and thanked law enforcement for its quick arrival. “Our deepest gratitude to law enforcement & first responders for their rapid response. Our hearts go out to all those injured & impacted today. We will come together to heal as a family,” she tweeted.

Echoing Wojcicki, Google CEO Sundar Pichai said in a tweet he had “no words to describe the tragedy that occurred today.”

Soon after news of the shooter broke, Google confirmed that it was in touch with authorities and evacuating the campus. It also urged employees there to shelter until further notice or avoid the area.

The US Bureau of Alcohol, Tobacco, Firearms and Explosives was also called to the scene.

President Donald Trump said on Twitter he had been briefed on the shooting, and that his thoughts and prayers were with everyone involved.

This story is developing.

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