Investigators in Nevada have found evidence indicating an intent to carry out a large-scale attack as well as white supremacist literature in the home of a man suspected of committing a deadly Sunday shooting at a festival in California.

The San Francisco Chronicle reported Tuesday that a search of 19-year-old suspect Santino William Legan's home in Walker Lake, Nev., turned up empty ammunition boxes, a gas mask, a knife, reading materials about radical Islam and white supremacy, and a camouflage backpack.

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Also found at the home was an empty bottle of Valium, according to the Chronicle. Authorities are now searching computers and other electronic devices at the home for more evidence of Legan's online activities and possible further connections to white supremacist movements.

“We continue to try to understand who the shooter was, what motivated him, and whether he was aligned with any particular ideology,” FBI Special Agent Craig Fair said at a press conference Tuesday, according to the Chronicle.

“Reviewing digital media, historically, has been very revealing in terms of somebody’s mind-set, ideological beliefs, intentions,” Fair continued. “We’ve got to get into the computers, the towers, the thumb drive, the phone, to get a holistic picture of him and who he was in touch with, what sentiments and thoughts he shared with others, what he cataloged for his own consumption.”

Three people were killed and more than a dozen were injured Sunday when a suspect, who police say was Legan, opened fire on the Gilroy Garlic Festival. One of the victims was just 13 years old.

The shooter used a semiautomatic rifle during the attack, according to police. Police say the rifle and a shotgun found in his car after the attack were purchased by Legan from gun stores in Nevada.

Legan was shot and killed by police.