It's being claimed that disturbed woman went on the killing rampage as a vendetta because YouTube were "censoring her videos and not paying her", according to a report in this morning's Daily Mail newspaper.
Nasim Aghdam walked onto the YouTube campus and started firing indiscriminately at 1pm local time yesterday, before turning the gun on herself.
"It was a woman and she was firing her gun. I just said, 'Shooter,' and everybody started running. It was terrifying," recounted one eye witness.
Im several tweets, another YouTube staff member Todd Sherman said: "We were sitting in a meeting and then we heard people running because it was rumbling the floor. First thought was earthquake.
"After existing (sic) the room we still didn't know what was going on but more people were running. Seemed serious and not like a drill.
'We headed towards the exit and then saw more people and someone said that there was a person with a gun. Shit.
"At that point every new person I saw was a potential shooter. Someone else said that the person shot out the back doors and then shot themselves.
"I looked down and saw blood drips on the floor and stairs. Peaked (sic) around for threats and then we headed downstairs and out the front."
Google CEO Sundar Pichai said that the shooting spree was an "horrific act of violence".
'Our thoughts and prayers are with everybody involved. Thank you to our phenomenal Law Enforcement Officers and First Responders that are currently on the scene,' he wrote on Twitter.
US President Donald Trump also took to Twitter last night and wrote: "Was just briefed on the shooting at YouTube’s HQ in San Bruno, California. Our thoughts and prayers are with everybody involved. Thank you to our phenomenal Law Enforcement Officers and First Responders that are currently on the scene."

Was just briefed on the shooting at YouTube’s HQ in San Bruno, California. Our thoughts and prayers are with everybody involved. Thank you to our phenomenal Law Enforcement Officers and First Responders that are currently on the scene.

— Donald J. Trump (@realDonaldTrump) April 3, 2018