Investigators may never know what drove shooter Santino William Legan to go on a shooting rampage at the Gilroy Garlic Festival, killing three people and wounding 16 others, a federal official said this week.

Law enforcement agencies have been scouring 19-year-old Legan’s digital footprint, including his social media presence, electronic devices and computer hardware seized both from his family’s home in Gilroy and a remote Nevada apartment where he’d been living since May, the Mercury News reported.

Federal investigators and FBI profilers nationwide are on the case — but even with all that in place, special agent-in-charge John Bennett said at a Thursday press conference that they have yet to nail down a motive.

“We have not yet determined [Legan’s] ideology,” he said, according to the report.

Authorities have been uncertain about whether extremist views played a role, after messages emerged that the teen posted to his Instagram shortly before the shooting, one of which encouraged people to read a 1980 white supremacy manifesto, and a second post referring to the local festival.

But it did not appear that he focused the gunfire on any particular group, the investigator added, according to the report.

“As we look at the injuries and the victims that are out there, it doesn’t seem clear that he was targeting any particular group,” he said. “It seems very random at this point.”

During the investigators’ raid of Legan’s apartment, they found a letter addressed to him by someone named “Virginia.” While they did not elaborate on details, the woman could be Santino’s maternal grandmother, Virginia Holden, who now goes by Virginia Prcic and lives in Southern California, the paper reported.

While a man who answered Prcic’s door confirmed her relationship to Legan, he told the outlet she last spoke to him and his brothers “10 years ago.”

“She saw it on the news. It’s just awful,” he told the paper. “Her blood pressure is going through the roof. She’s an old lady.”

Gilroy Police Chief Scot Smithee also said at the press conference that authorities identified a 16th shooting victim who had sought their own treatment for a graze wound, the paper reported.

He also identified the three officers who rushed to the scene of the Sunday massacre and fatally shot Legan: Eric Cryar, Hugo Del Moral and Robert Basuino, with 23, 17 and 13 years of experience on the force, respectively.

“I think they’re heroes,” Smithee said, according to the report. “I don’t think they’re particularly excited about being in the limelight, but I certainly think that they deserve recognition for what they did.”

Bennett, too, said the officers “really acted with tremendous courage.”

“Where most people run from gunfire, they ran toward it,” he said. “And that saved lives. There is no doubt.”