GILROY (CBS SF / CNN) -- Tinman lead singer Jack van Breen was stunned when he looked up and saw a man opening fire on the crowd with what looked like an assault weapon.
Van Breen, whose band was the last of the day and performing an encore at the annual Gilroy Garlic Festival, told KPIX 5 he heard someone shout, "Why are you doing this?" He said the person responded, "Because I'm really angry."
In a matter of minutes, the shooter's deadly volley had claimed three lives -- including a 6-year-old standing at a nearby bounce house -- and had wounded a dozen others.
CBS News has learned he has been identified as 19-year-old Santino William Legan. Authorities seized evidence from his father's home early Monday morning.
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An attendee in the crowd captured video of Van Breen's set when the shooting ensued. *WARNING: Possibly distressing footage*
Officers on the scene shot and killed the suspect within one minute of the shooting, according to police.
Police Chief Scot Smithee told reporters late Sunday night that the gunman armed with an assault-type rifle had evaded security by using "some sort of tool" to cut through a fence near a creek that borders a parking area.
"It's sort of a nightmare that you hope you never have to live in reality," he said calling the shooting "somewhat random."
An Instagram account, which was created four days ago under the suspect's name, posted two messages shortly before the attack began.
One included a photograph of people walking around the Garlic Festival with the words "Ayyy garlic festival time Come get wasted on overpriced sh**."
The other, which included a photo of Smokey the Bear and a sign saying "Fire Danger High Today," stated: "Read Might is Right by Ragnar Redbeard. Why overcrowd towns and pave more open space to make room for hordes of mestizos and Silicon Valley white tw**s?"
A mestizo is a person of mixed descent, commonly white and Hispanic or white and American Indian.
"Might is Right," first published in the late 1800s, has been described as a white supremacist text that promotes anarchy while vilifying Christianity. The book calls Jesus the "true Prince of Evil" and says that the natural order is a world at war in which the strong must vanquish the weak and white men must rule over those of color.
At a news conference on Monday, Smithee said that the weapon, an AK-47 type rifle, had been bought legally in Nevada earlier this month.
But the nightmare could have been worse. Smithee credited a heavy police presence for saving more lives as chaos descended on the decades-old food festival.
"We had many, many officers in the park at the time this occurred ... which accounts for a very, very quick response time," Smithee said.
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