By Christina Maxouris and Paul Vercammen, CNN

(CNN) -- [Breaking news update, 1:23 p.m. ET]

The suspect in the California food festival shooting used an assault-type rifle in his attack and was fatally shot by three officers who responded within a minute of the gunfire beginning, Police Chief Scot Smithee said at a news conference Monday.

The weapon, an AK 47-style rifle, was purchased legally in Nevada on July 9 of this year, he said.

A 6-year-old boy, a 13-year-old girl, and a man in his 20s were killed in the shooting, and police did not yet have a motive.

[Previous story, 12:57 p.m. ET]

(CNN) -- Instagram posts bearing the name of the suspected Gilroy Garlic Festival gunman mentioned a white supremacist book and showed a picture of people walking around the event shortly before the shooting began.

The suspect -- identified by two law enforcement officials as Santino William Legan, 19 -- killed three people in the Sunday evening attack, including a 6-year-old, and injured at least 12 others before he was fatally shot by police, authorities said.

He apparently entered the annual festival, which attracts about 100,000 people every year, by cutting through a back fence and then began shooting at random, Gilroy Police Chief Scot Smithee said.

Smithee credited a heavy police presence for saving lives as chaos descended on the decades-old festival in Gilroy, a city about 30 miles south of San Jose.

"We had many, many officers in the park at the time this occurred ... which accounts for a very, very quick response time," Smithee said.

Victims whose conditions ranged from fair to serious were transported to area hospitals, hospital officials said. Santa Clara Valley Medical Center received seven patients with gunshot wounds ranging in age from 12 to 69, according to Joy Alexiou, a spokeswoman for Santa Clara County Health System. Five patients remain in their care, including one in critical condition.

Witnesses reported seeing a second individual who has not yet been identified or found. Authorities haven't yet determined how the second person was involved, Smithee said. A manhunt is underway for that suspect, the chief said.

The killings were the latest addition to a bloody list of American mass shootings that have targeted anywhere and everywhere people congregate: at festivals, schools, places of worship, movie theaters, workplaces and bars.

An Instagram account bearing the suspect's name, created four days ago, posted two messages shortly before the attacks, including a reference to a white supremacist text.

One post was a photo of people walking around the Garlic Festival with the words "Ayyy garlic festival time Come get wasted on overpriced sh." The other post, made about an hour later, showed a sign of Smokey Bear saying "Fire Danger High Today."

"Read Might is Right by Ragnar Redbeard," the caption said. "Why overcrowd towns and pave more open space to make room for hordes of mestizos and Silicon Valley white tws?"

A "mestizo" is a person of mixed descent, usually white and Hispanic, or white and American Indian. "Might is Right" is a book published in the late 1800s which has been described as a white supremacist text that promotes anarchy, vilifies Christianity and calls Jesus the "true Prince of Evil." The natural order, according to the book, is a world at war in which the strong must vanquish the weak, and white men must rule over those of color.

They thought the pops were fireworks

Over the course of the three-day festival, families sampled garlicky foods like pasta con pesto and garlic-laced calamari and scampi, kids posed with festival mascot "Herbie" and a series of musicians performed, including Colbie Caillat and her band, Gone West.

The pop-pop-pop of gunfire began around 5:41 p.m. Sunday as the rock band TinMan played its last song.

"We ran off the stage (and) we crawled underneath it," TinMan singer Christian Swain said. "We could smell the gunpowder."

Videos of the aftermath show crowds of people screaming and fleeing as they sought safety.Lex De La Herran was walking away as the music on stage had begun winding down, he said.

"I turned around for a quick moment and I hear the gunshot sounds," he said. "At first I thought it was fireworks but a man behind me screamed that 'those are real, those are real.'"

"I just froze like a deer in the headlights," he said.

De La Herran said a piece of shrapnel hit him in the head. Then, he started running among the crowds.

"I saw people jumping over the fence, people trampling over each other, it was just widespread chaos," he said. "People were definitely in shock ... some people were visibly shaking."

Cynthia Saldivar also said she initially thought the sounds were fireworks.

"We looked toward the area that it was coming from and everyone stood still for a second and realized it was gunshots," she told CNN. "Everyone started running out towards us up the hill to the street to be safe. Then I saw some people shot, some doing CPR on others."

It felt like a nightmare, Miquita Price said.

The shooter stood about 15 feet away from her and was blocking her only possible escape route, she told CNN.

"I started running, we hit the ground and I literally laid down on the ground," she said. The shooter stopped firing for a couple of seconds, multiple people reported, and when he began to shoot again, Price said she took off running.

The woman running next to her was hit and Price said she continued until she found a truck to hide behind.

She's still in shock.

"(There) was blood everywhere," she said. "I read about this but I never thought I would be in it."

A 7-year-old boy whose parents are funnel cake vendors told CNN affiliate KPIX that he hid under a table until police got to the suspect.

"I thought I was going to die," Paul Davies said.

A 6-year-old killed

Stephen Romero, 6, was killed during the shooting, Gilroy City Councilmember Fred M. Tovar told CNN.

Tovar said he was "deeply saddened by the news."

"I pray that God will grant his family strength. My most sincere condolences. I will keep your family close in my thoughts and prayers in the coming weeks as you are going through the process of grieving," he said in a statement.

Stephen's grandmother spoke to CNN affiliate KRON about the boy's death.

"This is really hard, there's no words to describe (it)," Romero's grandmother told the affiliate. "He was such a happy kid, I don't think that this is fair."

Stephen's father, Alberto Romero, told CNN affiliate the San Jose Mercury News newspaper that he was at home when his wife called to say that she, her mother and their son had been shot.

"I couldn't believe what was happening, (I thought) that what she was saying was a lie, maybe I was dreaming," he said.

The dad went to a hospital to see his son.

"They told me he was in critical condition and that they were working on him," he said. "Five minutes later they told me he was dead."

Officers confronted suspect in minutes

Swain said police seemed to secure the area within five minutes from when the shooter began firing.

"We know the event was well-covered with security and we'd seen them as we came in to set up and play," he told CNN. "At least in my head, I knew they would be there and sure enough that seems to be what happened."

Officers were in the area when the shooting began, Smithee said, and engaged the suspect "in less than a minute."

"I can't speak enough about the courage of police and first responders are showing at this moment," Tovar said. "My thoughts and prayers are with the families of those who (lost) their lives, and those recovering in the hospital."

Chief Smithee said it appeared that the suspect entered the festival via a creek that borders a parking area. The suspect used a tool to cut through a fence and get into the area undetected.

Police recovered a firearm and rifle ammunition from the shooting scene, a law enforcement source told CNN.

The FBI Evidence Response Team from San Francisco arrived on scene late Sunday night, a law enforcement official told CNN. ATF's San Francisco Field Division is also assisting in the case.

"It is just incredibly sad and disheartening that an event that does so much good for our community has to suffer from a tragedy like this," Smithee said.

'Our annual family reunion'

The multi-day festival attracts about 100,000 people annually to Gilroy, the self-proclaimed garlic capital of the world, according to attendance records. There's food, live music, cooking competitions and thousands of community volunteers who bring it all together.

The event has raised more than $11.7 million for local charities since 1979, organizers said. In 2018, organizers donated more than $255,000 to 170 different groups, including churches and school sports teams.

This year -- the festival's 41st -- featured celebrity chefs Tom Colicchio of "Top Chef" and Gerron Hurt of "MasterChef."

"To have seen this event end this way this day is just one of the most tragic and sad things that I've ever had to see," Gilroy Garlic Festival Executive Director Brian Bowe said.

Gilroy, a city of about 58,000 people, is a "tightly-knit," family-like community, Bowe said.

"And for over four decades that festival has been our annual family reunion," he said Sunday.

Shawn Keck, president of the 2019 Gilroy Garlic Festival, thanked the police and first responders who came to their aid.

"We are heartbroken that senseless violence brought this year's festival to such a terrible and tragic end," he said in a statement.

How politicians responded

President Donald Trump expressed "our deepest sadness and sorrow for the families who lost a precious loved one" in the shooting, he said in the Rose Garden on Monday.

Trump called the perpetrator "a wicked murderer" who "opened fire and killed 3 innocent citizens, including a young child."

"We're praying for those who are recovering right now in the hospital," Trump said, before thanking "the brave members of law enforcement."

A number of 2020 Democratic presidential candidates also reacted to the shooting.

California Sen. Kamala Harris said she was "grateful to first responders who are on the scene in Gilroy and keeping those injured by such senseless violence in my thoughts."

"My office is closely monitoring the situation," she tweeted.

Late Sunday night, former Vice President Joe Biden said "this violence is not normal."

"How many more families will have to lose a loved one before we fix our broken gun laws? We must take action, starting with real reform. Our thoughts are with everyone in Gilroy this evening. Enough is enough," he said.