Fresno police are doubting the credibility of a bomb threat made at Edison High School on Thursday.
Police Lt. Mark Hudson said there was graffiti that suggested a bomb was on campus.
He said police cleared an area of the campus to ensure nothing was there.
The threat was spotted about 9 a.m. in a campus bathroom, said Jessica Baird, Fresno Unified School District spokeswoman.
Students were not taken out of class, and police remained on campus throughout the morning as a safety precaution, she said.