MONTEBELLO (AP) — Police in Montebello say a phony bomb threat forced thousands of high school students out of class for about three hours.

Lt. Luis Lopez says a young male caller using a payphone warned authorities shortly before 8 a.m. Monday that there was a bomb in a building at Schurr High School.

Youngsters were taken to the athletic field and held there while a Los Angeles County sheriff’s bomb squad searched the campus. No bomb was found and the all-clear was given after about three hours.

Lopez says investigators will try to determine which payphone was used to call in the threat. They’re hoping video may be available to help identify the suspect.