Police in Mountain View, California, said they didn't notice anything alarming after encountering the YouTube shooter the morning of the attack.
Officers found Nasim Aghdam in her car in a parking lot around 1:40 a.m. Tuesday.
"At no point during our roughly 20 minute interaction with her did she mention anything about YouTube, if she was upset with them, or that she had planned to harm herself or others," Mountain View police said. "Throughout our entire interaction with her, she was calm and cooperative."
Police called Aghdam's father and brother, but "at no point did her father or brother mention anything about potential acts of violence or a possibility of Aghdam lashing out as a result of her issues with her (YouTube) videos," the department said.
[Breaking news update at 12:26 p.m. ET]
The woman who shot three people at YouTube headquarters Tuesday did not have a link or relationship with the three people she shot, San Bruno Police Chief Ed Barberini said Wednesday.
"We know she was upset with YouTube, and now we've determined that was the motive," Barberini said.
The police chief also said the assailant, Nasim Najafi Aghdam, visited a shooting range before the attack. Police said they found a Smith & Wesson 9mm gun registered to her at the scene.
[Previous story, published at 9:37 a.m. ET]
The brother of Nasim Najafi Aghdam worried she might do something dangerous.
The concerns started over the weekend when Aghdam stopped answering her phone, her brother told CNN affiliate KGTV. Then the San Diego resident's car was found more than 700 miles northwest, in Mountain View, California.
"I Googled 'Mountain View,' and it was close to YouTube headquarters. And she had a problem with YouTube," said Aghdam's brother, who did not want to be identified.
So he called police to say "she went all the way from San Diego, so she might do something."
That fear turned into reality Tuesday afternoon when Aghdam shot three people at the YouTube campus in San Bruno before killing herself with a handgun.