UPDATE | Gunman posted online minutes before killing 3 at festival

GILROY, Calif. (AP) — Before a 19-year-old gunman opened fire on a famed garlic festival in his California hometown, he urged his Instagram followers to read a 19th century book popular with white supremacists on extremist websites, but his motives for killing two children and another young man were still a mystery Monday.

Santino William Legan posted the caption about the book "Might is Right" with a photo of Smokey the Bear in front of a "fire danger" sign. He posted another photo from the Gilroy Garlic Festival minutes before he shot into the crowd Sunday with an "AK-47-type" weapon, killing a 6-year-old boy, a 13-year-old girl and a recent college graduate.

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 the shooting injured 12 others and sent 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 gun 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 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 searching for clues as to what caused the son of a prominent local family to go on such 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.