On Tuesday, a shooter opened fire at YouTube's headquarters in San Bruno, California.

Many YouTube employees had no idea there was an active shooter nearby as they evacuated their offices after a fire alarm went off.

Zachary Vorhies, a senior software engineer, jumped on his electric skateboard and found himself at the scene of the shooting.

On Tuesday, a woman opened fire with a handgun at YouTube's headquarters in San Bruno, California, injuring three people — one of them critically — and killing herself, police said.

Many employees calmly exited their offices when they heard a fire alarm, not knowing there was an active shooter nearby. Zachary Vorhies, a senior software engineer at YouTube, said he and his coworkers grabbed their stuff and left the building when the alarm went off.

Vorhies jumped on his electric skateboard and headed down a hill. He soon arrived at an internal courtyard, where he saw a man on the ground.

"He had a red spot on his stomach, and he was lying on his back, not moving," Vorhies, 37, told The New York Times. "I saw the blood soak through the shirt."

He also said he saw a large man, wearing gray, yelling "Do you want to shoot me?" and "Come at me!"

"I just was like, what's going on?" Vorhies told NPR, adding that he didn't realize the man on the ground had been shot.

Shortly afterward, he said, the door between the courtyard and the street swung open, and a police officer with an assault rifle barged in.

"At that point, I realized this was not someplace I needed to be," Vorhies told NPR.

He grabbed his skateboard and escaped into an adjacent parking structure. In a nearby parking lot were a couple hundred of his coworkers who had evacuated.

Authorities in San Bruno on Tuesday night identified the shooter as Nasim Aghdam, a 39-year-old San Diego resident. Aghdam appeared to be critical of YouTube in many posts on social media accounts linked to her.