A search of the home of Santino Williams Legan, the man law enforcement says shot and killed three people at the Gilroy Garlic Festival, has turned up materials on white supremacy and radical Islam, according to a report from the San Francisco Chronicle.

Federal law enforcement sources told the Chronicle that the makings of "massive attack" were found in the Walker Lake, Nevada rental home where the shooter was staying. Among the items found were a gas mask, "numerous" hard drives, a bulletproof vest and "reading material on white supremacy and radical Islam."

An Instagram account purportedly belonging to the shooter also referenced white supremacist ideology, recommending "Might is Right" by Ragnar Redbeard.

Written under a pseudonym in the late 1800s, the book is a defense of Anglo-Saxon and male supremacy, and argues that weakness shows moral inferiority. It is also full of anti-Semitic rhetoric.

"It's widely popular and present among ethnocentric white nationalists of all levels, from suit-and-tie white supremacists to neo-Nazis," Keegan Hankes, a senior analyst for the Southern Poverty Law Center's intelligence project, told Rolling Stone.

MORE: Nevada store owner who sold Gilroy shooting suspect the gun: 'I hope you rot in hell'

Federal and local law enforcement are still investigating Legan's motives.

"I would say that we are not closer to understanding that motive, what happens within the psyche of a 19-year-old kid. I can't speak to that," Craig Fair of the San Francisco FBI office told the Associated Press. "Determining the motive is an exceptionally important thing for law enforcement to try to understand one, why they did it, and two, are they acting in collaboration with any other individuals. Are they inspired by some other organization? Were they radicalized online? What were the real factors that induced this person to take this kind of heinous action."

Police say Legan circumvented festival security by using a tool to cut through a fence near the parking lot at Christmas Hill Park on Sunday. Once inside, he opened fire at 5:41 p.m., killing three. Police officers, already on the scene to provide support for the food festival, confronted the suspect in less than a minute. Smithee says three officers shot and killed Legan.

The three victims were identified as Stephen Romero, 6, Keyla Salazar, 13, and Trevor Irby, 25.

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Katie Dowd is an SFGATE Senior Digital Editor. Contact: katie.dowd@sfgate.com | Twitter: @katiedowd