UPDATE: Tombstone High School has been declared safe. The school is back open.
Cochise County said no one has been taken into custody.
Tombstone High School was evacuated Thursday due to a bomb threat.
According to the school's Facebook page, students were shifted to Walter J. Meyer School, 411 N. 9th Street in Tombstone.
Tombstone High is located at 1211 N. Yellow Jacket Way.
Authorities investigating include the Tombstone Marshals, Fort Huachuca EOD K-9 team, Geronimo air support and Cochise County Sheriff's Office. Law enforcement teams conducted a sweep of the school.