BOTHELL, Wash. -- A Bothell High School woodshop teacher was struck in the back of the head and had a zip tie placed around his neck in an on-campus assault Thursday, police said. The Northshore School District canceled classes Friday as a precaution and to allow police to investigate.

Bothell Police spokesman Sgt. Ken Seuberlich said Friday the teacher, identified by the district as 63-year-old Cal Pygott, was assaulted during after-school activities Thursday near a classroom with a blunt object.

Another staff member found Pygott stumbling outside the classroom, removed the zip tie and called 911. He was taken to Harborview Medical Center with serious injuries and released Friday.

Seuberlich could not say if the zip tie blocked Pygott’s airway.

Police locked down the campus for two hours to search for suspects but found nothing. No suspects have been identified.

Detectives are looking at video surveillance cameras in the school to identify a suspect.

“This is a highly unusual event,” said Seuberlich, a former school resource officer.

Seuberlich could not say if Pygott were the target of previous threats.

"I was really pissed off, honestly, because I don't know who would do something like that to someone who is so nice," said former student Tim Smith when he heard about the assault."He's really stand up. If I ever needed anything I would always go to him. I liked him so much I took three years of his classes. Sometimes two periods at a time. He's just a really great guy."

“This is an alarming – and highly unusual – situation,” said Northshore Superintendent Larry Francois in a statement. “While the BHS school community faces the greatest impact, the concerns for student and staff safety naturally extend to all Northshore school communities.

“Times like this remind us of the importance of standing together and supporting one another when one branch of the Northshore family tree experiences such a tragic event,” Francois continued. “Over my eight years as Northshore superintendent, I have time and again witnessed our students, staff and families demonstrating the best qualities of this compassionate and caring community in response such events. Through gestures large and small, the support you provide to those most impacted means more than you may ever know.”

School will resume Monday. Students and staff are being asked to wear blue in support of Pygott.

Anyone with information is asked to call the tip line at 425-487-5551 or contact Bothell Police via Twitter @BothellPolice.

The school district is suggesting these resources for students and parents who may be feeling anxiety from this assault.

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