After conducting an extensive search Wednesday night, the Flathead County Sheriff’s Office determined that a bomb threat at Bigfork High School had no validity.

Bigfork Superintendent Matt Jensen said administrators learned of the threat Wednesday just after 3:40 p.m. It was written in graffiti in the science lab at Bigfork High School.

Jensen said school officials immediately informed the Sheriff’s Office, which worked with a private bomb detection service to search Bigfork schools.

Jensen said classes were already finished and any students remaining in the building for after-school activities were evacuated before the search began.

According to the Sheriff’s Office, the Montana Highway Patrol and the U.S. Forest Service assisted in the evacuation.

The search ended just after 9:30 p.m., according to a message sent out by school officials.

No bomb was found and the schools opened at their regular time on Thursday.

“I’m confident this was a hoax, but we take things like this very seriously,” Jensen said. “We are going to make sure the individual responsible knows it’s unacceptable and completely inappropriate.”

Both school officials and the Sheriff’s Office are still investigating who wrote the threatening graffiti.