Man who wanted 'We love ISIS’ hat convicted in rifle case

David Diaz Sr. David Diaz Sr. Photo: San Mateo County Sheriff / San Mateo County Sheriff's Offic Photo: San Mateo County Sheriff / San Mateo County Sheriff's Offic Image 1 of / 1 Caption Close Man who wanted 'We love ISIS’ hat convicted in rifle case 1 / 1 Back to Gallery

A 54-year-old San Mateo man with apparent mental health issues pleaded no contest to possessing an automatic assault rifle, in a case that began when he went to a mall to get a hat embroidered with “We Love ISIS,” a prosecutor said Friday.

David Diaz Sr., who told authorities he is a military veteran who suffers from post-traumatic stress disorder, entered his plea Thursday before Judge Jonathan Karesh of San Mateo County Superior Court to a felony count and was not expected to serve any prison time, said District Attorney Steve Wagstaffe.

Instead, Diaz was referred to Veterans Treatment Court, which provides veterans with mental health treatment. He is free in lieu of $175,000 bail.

On Oct. 7, Diaz went to the Lids hat store at the Hillsdale Shopping Center in San Mateo and asked that his hat be embroidered with “We Love ISIS,” Wagstaffe said. Diaz questioned the clerk about her religion and other personal matters, Wagstaffe said, before telling her, “Millions of Americans are going to die because America can’t mind its f— business.”

Diaz purportedly told the clerk he was a member of the terrorist group the Islamic State, which is also known as ISIS, and had beheaded 97 nuns. The clerk told Diaz she was going to have to check with her superiors, and he left, Wagstaffe said.

The clerk called San Mateo police the next day, prompting officers and FBI agents to visit Diaz’s apartment on George Avenue. They learned he was on numerous psychiatric medications, Wagstaffe said. Diaz told the investigators that he was a veteran suffering from PTSD and “denied loyalty to ISIS,” the prosecutor said.

Diaz was placed on an involuntary psychiatric hold, and authorities confiscated six rifles and two handguns, including an illegal assault rifle and a sawed-off shotgun, Wagstaffe said. Officers also reporting seizing thousands of rounds of ammunition and five illegal high-capacity magazines.

Henry K. Lee is a San Francisco Chronicle staff writer. E-mail: hlee@sfchronicle.com Twitter: @henryklee