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The first gunshots were heard around 5:40pm local time, immediately causing confusion and panic at Gilroy's Christmas Hill Park in Santa Clara County.

"We heard it distinctly. I just didn't recognize the first round. The second time I did, [when] they were getting closer," a witness told local media. "I just started running. I left everything and ran."

Videos shared online show people abandoning food stands and fleeing the park in fear, with bangs heard in the background. The Gilroy Garlic Festival is a popular family event in California, and many were there with small children when the shooting started.

Santino William Legan posted the caption about the book "Might is Right," which claims race determines behavior. It appeared with a photo of Smokey the Bear in front of a "fire danger" sign and also complained about overcrowding towns and paving open space to make room for "hordes" of Latinos and Silicon Valley whites.

In his last Instagram post Sunday, Legan sent a photo from the Gilroy Garlic Festival. Minutes later, he shot into the crowd with an AK-47 style weapon, killing a 6-year-old boy, a 13-year-old girl and a man in his mid-20s.

Under it, he wrote: "Ayyy garlic festival time" and "Come get wasted on overpriced" items. Legan's since-deleted Instagram account says he is Italian and Iranian.

The postings are among the first details that have emerged about Legan since authorities say he appeared to fire at random, sending people running and diving under tables. Police patrolling the event responded within a minute and killed Legan as he turned the weapon on them.

He legally purchased the semi-automatic assault rifle this month in Nevada, where his last address is listed. He would have been barred from buying it in California, which restricts firearms purchases to people over 21. In Nevada, the age limit is 18.

Legan grew up less than a mile from the park where the city known as the "Garlic Capital of the World" has held its three-day festival for four decades, attracting more than 100,000 people with music, food booths and cooking classes.

Authorities were looking for clues, including on social media, as to what caused the son of a prominent local family to go on a rampage. His father was a competitive runner and coach, a brother was an accomplished young boxer and his grandfather had been a supervisor in Santa Clara County.

Police said they don't know if people were targeted, but at this point, but it appears he shot indiscriminately. Twelve people were injured.

Police searched Legan's vehicle and the two-story Legan family home, leaving with paper bags. Authorities also searched an apartment they believed Legan used this month in remote northern Nevada. Officials didn't say what they found.

The city had security in place for one of the largest food fairs in the U.S. It required people to pass through metal detectors and have their bags searched. Police, paramedics and firefighters were stationed throughout the festival.

But Legan didn't go through the front entrance. He cut through a fence bordering a parking lot next to a creek, Gilroy Police Chief Scot Smithee said. Some witnesses reported a second suspect, and authorities were trying to determine if he had any help.

Police arrested a 20-year-old man who claimed involvement online, but investigators determined he was just trying to get attention.