“Anti-Islamic writings” were found in a vehicle connected to the two teenage suspects in Monday’s shooting at the Islamic Center of San Diego that killed three people, according to a Department of Justice official with knowledge of the investigation.

The alleged gunmen have been identified as Caleb Vasquez, 18, and Cain Clark, 17, the official told Reuters on Tuesday. They were found dead in their car after the shooting, apparently from self-inflicted gunshot wounds, police said on Monday.

Police said the attack was being investigated as a hate crime but declined to offer further details about a possible motive.

Clark’s mother is cooperating with authorities, the DOJ official added. Officers sprang into action on Monday after a call from one of the boy’s mothers, who described her son as suicidal and said he had run off with her vehicle and three of her guns, according to police.

Police initially raced to a local shopping mall and the boy’s school before calls came in about the shooting at the mosque.

The Islamic Center is the largest mosque in San Diego County, California, and houses the Bright Horizon Academy. All students were safe and accounted for after Monday’s attack.

Rick Rodriguez, 69, was working in his driveway near the mosque on Monday when he heard the sound of helicopters. “I feel for all the people and kids, and now they have to think about this the rest of their lives,” he said.

A fundraising effort organized by CAIR San Diego with the Islamic Center of San Diego has raised over $1.7 million for the family of slain security guard Amin Abdullah, who authorities have credited with preventing further bloodshed.

Ahmet Kuru, a political science professor at San Diego State University, attends the mosque and knew Abdullah, who he called a “hero” and beloved community member. Reuters