No explosives were found on Los Altos High School's campus in an extensive search Friday, Oct. 1, after the school received a bomb threat in the morning.

A caller contacted the school at 8:55 a.m. Friday saying there were explosives on campus, Santa Clara County Fire Department spokesperson Justin Stockman said. The Los Altos Police Department was notified at 9 a.m. and students and staff were evacuated soon thereafter.

Law enforcement and other first responders conducted a multi-hour search of the campus, using explosive-detecting dogs to check for possible bombs.

Students and staff, meanwhile, were evacuated onto the campus fields and kids were subsequently released to their parents.

Several homes on Alicia Way near the school were evacuated and Almond Avenue was closed between Valencia Drive and Sunkist Lane.

Almond Elementary School and Egan Junior High School, which are nearby, remained open, Los Altos city spokesperson Sonia Lee said.

"The threat was specific to the high school," she said.

At roughly 2 p.m., emergency personnel finished clearing the high school campus and determined that there were no explosives present, Stockman said.

"The investigation has determined there was not an incendiary device on campus, but the investigation into the school disruption is still ongoing," Superintendent Nellie Meyer said.

Students had just begun their school day when the campus was evacuated. According to Los Altos High student Tomo Chien, an administrator came over the PA system to announce that everyone needed to evacuate.

Students were at first taken to the turf football field, then to the portion of the track furthest from the classroom buildings and then to the baseball diamond, Chien said. Students subsequently moved back to the track, Stockman said.

Staff handed out water and Chien described the situation among students as calm.

"They're saying we're all safe," Chien said Friday morning. "The police and fire department need to go check rooms one-by-one."

Stockman characterized the search as an "intense process" that involved checking "every possible place that a device could be hidden or left." The use of explosive-detecting dogs sped the process along.

"If we had to do it with people, it could take a very, very long time," Stockman said. "The use of K-9s means that we don't have to go into every single cupboard and hidden area, because the dogs have such an acute (sense of) smell for the explosives that are typically used."

He stressed that any bomb threat is serious and considered credible, with the involvement of a large school heightening the concern.

Both a primary and secondary search was done of the full campus, with multiple dogs checking each location, Stockman said. The effort involved local police and fire departments, as well as federal agencies including the Department of Homeland Security and the U.S. Coast Guard.

The motive for the bomb threat isn't yet known, Stockman said, but he stressed that law enforcement will be undertaking a serious investigation in the days and weeks ahead.

"A bomb threat is not a prank. It's a real disruption for the community and it will obviously be prosecuted aggressively," he said.

The search took nearly the entire school day. Students were able to come to pick up their bikes or cars on Friday afternoon, Assistant Principal Suzanne Woolfolk wrote in an email to students and parents. Belongings in classrooms, including backpacks, cell phones, laptops and textbooks, won't be available for pick-up until Monday. There's an exception for items needed immediately, such as medications, which can be retrieved sooner, Woolfolk wrote.

Given the disruptions, no homework will be assigned this weekend. On Twitter, Chien wrote that there were "big cheers" from students when the homework-free weekend was announced.

Woolfolk, Meyer and Stockman all stressed that school staff, students and parents did a good job of following the emergency protocols that have been put in place.

"If we take nothing else away from what happened today, it's that we all need to plan ahead for the unexpected," Stockman said. "Whether it's bombs or wildfire or a pandemic, we need to be prepared as a community for unexpected things to happen."