A bomb threat caused authorities to place East High School under lockdown for three hours on Thursday.

Police and the fire department were called to the school at 10:45 a.m. after the threat came from a cell phone caller.

Bomb sniffing dogs from several law enforcement agencies searched the building. 

When sweeps determined that some parts of the building were safe, students were moved to that area while the search continued in other portions of East High.

The all clear was given just before 2 p.m. when no explosive device was found.

Authorities are working to find out who phoned in the threat.