A high school student in California was arrested and is facing attempted murder charges in a plot to carry out a shooting on campus that was uncovered after a classmate expressed concerns the teen was “fixated on school shootings and had access to weapons,” police said.

Sebastian Villasenor, 18, was arrested Saturday and at his home investigators found seven rifles, two revolvers, a handgun and a shotgun, along with more than 1,000 rounds of ammunition, Ontario Police Chief Mike Lorenz said at a news conference Wednesday.

Villasenor had five intended victims – all students – and was considering a sixth, Lorenz said. The five intended victims were girls, according to a criminal complaint.

Villasenor “had every intention of carrying out a school shooting,” Lorenz said. He “was obsessed with school shootings and police response times. He researched tactical supplies and was in the process of choosing a specific date.”

Villasenor is charged with one count of attempted criminal threats and five counts of attempted murder, according to the complaint and a news release from the San Bernardino County District Attorney’s Office.

CNN is working to identify Villasenor’s legal representation. He is scheduled to be arraigned Thursday, the district attorney’s office said. He is being held without bail, jail records show.

The investigation began February 8 when officials from Ontario Christian High School contacted police after a student reported concerns about a classmate, Lorenz said. Ontario is about 40 miles east of Los Angeles.

“This student bravely … shared their fear that they and others could be harmed by Villasenor,” the police chief said. “That student saved lives, spared families from losing their children, and the community from being devastated from a senseless act of violence.”

Ben Dykhouse, principal of the private school, said he was grateful the student was “brave enough to say something when they saw something that was off.”

In regards to a potential motive, police determined through interviews Villasenor “was not bullied or harassed. He did, however, have difficulties in forming relationships with other students and in his social interactions.”

Investigators believe Villasenor was planning to carry out the shooting sometime around April 20, which is the 25th anniversary of the Columbine shooting. The teen “had an obsession” with the 1999 shooting at a Colorado high school, which left 13 people dead, Lorenz said.

“April 20 this year happens to be on a weekend, so we believe it was going to be some time around that time frame,” the chief said.

The news conference announcing the arrest was held the same day survivors and victims’ loved ones were marking six years since a student opened fire at Parkland High School in Florida, killing 17 people and wounding 17 others. As of last week, there have been at least eight shootings on K-12 campuses in the US in 2024, according to a CNN analysis, following at least 52 shootings last year.

As the pace of campus violence remains high, prosecutors are testing the limits of who can be held responsible when a student opens fire on classmates, including the recent conviction of Jennifer Crumbley on involuntary manslaughter charges in Michigan after her son killed four students in a 2021 shooting at Oxford High School.