Updated at 4:48 p.m. ET
The FBI has opened a domestic terrorism investigation into last month's mass shooting at the Gilroy Garlic Festival in California, after discovering that the shooter had a list that may have indicated potential targets of violence.
The investigators are still trying to determine a motive for the attack. At this point, "we have uncovered evidence throughout the course of our investigation that the shooter was exploring violent ideologies," John Bennett, special agent in charge of the FBI's San Francisco Field Office, said at a news conference Tuesday.
The gunman, 19-year-old Santino William Legan, killed three people, including two children, when he opened fire on July 28. The shooter also died from a self-inflicted gunshot wound, police have said.
Legan appeared interested in multiple violent ideologies, Bennett said. Investigators are trying to determine "what if any ideology he had actually settled on" and "who, if anyone, he may have been in contact with regarding these ideologies," Bennett said.
They are also trying to determine whether anyone else knew about the attack beforehand, Bennett said, and "why he committed this specific act of violence."
A list of organizations found on the shooter's digital media, which Bennett says may have been potential targets, includes "religious institutions, federal buildings, courthouses, political organizations from both major political parties, and the Gilroy Garlic Festival."
Bennett said that for the FBI to open a domestic terrorism investigation, there must be a potential federal violation, the threat or unlawful use of force or violence, and "most importantly, the existence of ideological motivation."
At the same news conference, Gilroy Police Chief Scot Smithee said that police have concluded the shooter fired 39 rounds.
Three police officers engaged the gunman less than a minute after he started firing — and Smithee told reporters that those officers fired 18 rounds. Some of them hit the gunman, though authorities have said that he was ultimately killed by his own hand.
He was wearing a bullet-resistant vest, Smithee said, and carrying multiple magazines. In his backpack, police officers found a rifle scope and a flashlight.
Smithee also said that investigators have determined that none of the victims who were killed were hit by police fire — they were all killed by the gunman.