An AWOL Navy corpsman turned himself in Wednesday after leaving a threatening note claiming he planted bombs at a nearby Southern California high school in an incident that prompted administrators to order students out of the building on the first day of classes.

Daniel Morgan, 22, surrendered at Camp Pendleton Marine Corps base at around 1 p.m. Wednesday, Master Sgt. Mark Oliva said.

Morgan was last seen at the base at 5 p.m. Tuesday, Orange County sheriff's spokesman Jim Amormino said. When he failed to show up for work Wednesday morning, his barracks were searched and a note was discovered, he said.

Morgan wrote that he had placed explosive devices in and around San Clemente High School, which is located just a few miles from one of the gates to Camp Pendleton, Amormino said.

Soon after the note was found, about 3,200 students and 180 faculty members were told to leave the school's buildings. Students and staff waited on the school's football field — and later in the gymnasium, auditorium and other rooms — as bomb squads searched through buildings and classrooms. After about four hours, everyone was sent home.

"The campus is secure," Amormino said at around noon. "We have every available bomb-sniffing dog in the county here searching room by room."

Later Wednesday, a Marine spokesman said no military-grade explosives were missing from the base, and sheriff's Lt. Roland Chacon said no explosives or suspicious devices were found at the school during a five and a half hour search.

Morgan was being interviewed by military authorities and could face a military charge of unauthorized absence after failing to report to duty, Oliva said.

"It's weird, you don't think someone who's supposed to be protecting our country would put all of our kids in danger," student Megan Lombardy told KCAL-TV.