By Faith Karimi and Holly Yan, CNN
(CNN) -- [Breaking news update at 12:38 p.m. ET]
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.
But it's unclear whether the brother's concerns were relayed to authorities in the Bay Area, San Bruno police Chief Ed Barberini told ABC's "Good Morning America" on Wednesday.
"We know that she was reported missing by her family in San Diego on the 31st of March, and that she was located in a community about 30 miles south of us early Tuesday morning," Barberini said.
"I don't know what concerns were conveyed to that police department, or how or where those concerns were relayed to. So that is something we're looking into."
Website reveals angst against YouTube
Authorities gave conflicting accounts of whether Aghdam knew any of her three victims, who are hospitalized in fair, serious and critical condition.
Shortly after the shooting, two law enforcement officials told CNN the shooter knew at least one victim. But on Tuesday night, police said they have no evidence Aghdam knew any of the victims or whether they were targeted.
Barberini said the motive remains uncertain. But police are investigating a website that appears to show the same woman accusing YouTube of restricting her videos, according to the Los Angeles Times.
CNN is working to confirm the authenticity of the website, which lists four YouTube channels: one in Farsi, one in Turkish, one in English and one devoted to hand art. It also lists an Instagram page that focuses on vegan life.
The woman's grievances against YouTube appear to focus on censorship and revenue.
"There is no equal growth opportunity on YOUTUBE or any other video sharing site, your channel will grow if they want to!!!!!" one post reads. "Youtube filtered my channels to keep them from getting views!"
Another post accuses "close-minded" YouTube employees of putting an age restriction on videos, saying it's aimed at reducing views and discouraging the woman from making new videos.
Shooter yelled: 'Come get me!'
The gunfire started shortly before 1 p.m. at the company's headquarters about 10 miles from San Francisco.
Senior software engineer Zach Voorhies bolted when the fire alarm blared.
"I went outside with my electric skateboard and I started skating down, because I thought it was a fire," he told CNN affiliate KPIX. "I heard some yelling and I saw somebody down on his back with a red spot on his stomach."
As they fled the building, he said, the shooter was in the courtyard yelling, " 'Come at me, or come get me!' "
Product manager Todd Sherman said he was at his desk when he heard what sounded like rumbling as people ran.
"First thought was earthquake," Sherman said in a series of tweets. He dashed toward the exit, where someone said there was a person with a gun.
"At that point, every new person I saw was a potential shooter," he said. "I looked down and saw blood drips on the floor and stairs."
He fled downstairs, peeking around him to ensure the shooter was not around before dashing out of the building.
A sprawling tech complex
YouTube was founded in February 2005 and quickly became a major site for online videos. It was later purchased by Google.
More than 1,100 people work at the YouTube campus in San Bruno. Employees there include engineers for the site and sales teams that work with advertisers and content creators.
Google CEO Sundar Pichai sent a message to employees following the shooting.
"I know a lot of you are in shock right now," ," Pichai said. "Over the coming days, we will continue to provide support to help everyone in our Google family heal from this unimaginable tragedy."
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