On Thursday, his 16th birthday, a Southern California high school student brought a gun to school in his backpack and started shooting.

He killed a girl, 16, and a boy, 14, and wounded at least three other students, some critically, and later turned the .45 caliber semi-automatic pistol on himself, according to the Los Angeles County sheriff’s department.

The shooter was taken to a hospital with a head wound, his condition described as “grave.”

The sheriff’s office described the wounded as two girls, ages 14 and 15, and one boy, 14.

It was at least the 11th school shooting in the U.S. this year and at least the 10th mass shooting in California since 2013.

Thursday’s attack began around 7:30 a.m. Pacific Time, at Saugus High School in Santa Clarita, 30 miles northwest of downtown Los Angeles.

The school remained in lockdown with many students inside for more than an hour while authorities searched for and apprehended the shooter, also recovering a weapon. It’s unclear where the suspect was located.

Harrison Simpson, the father of one student caught in the lockdown, said his 15-year-old daughter was “freaked out,” reports the Los Angeles Times. “She’s scared. I don’t know if she’s going to want to go back.”

Just two months ago, six students at Saugus High were detained on felony criminal charges after authorities were alerted to threats they had made online. It’s unclear if those threats were connected to Thursday’s attack, the LA Times says.

“Former U.S. Rep. Katie Hill stood in her backyard … as helicopters circled overheard searching for the gunman,” the newspaper says, noting that Hill graduated from Saugus High 15 years ago, before active shooter drills were being discussed and practiced.

“I’m absolutely horrified that it’s happening at my school,” she said.