NEVADA -- Story County sheriff's officers evacuated both the Story County Justice Center and the Story County Administration Building this morning after an as-yet unknown caller phoned a bomb threat into dispatch.

Sheriff Paul Fitzgerald said the call, which came in through the emergency lines at about 8:17 a.m., was a male voice stating there were two explosive devices outside "the courthouse" and they would be detonated.

Officials quickly evacuated both the justice center and the administration building, which houses most of the non-law enforcement county offices and is considered by many in the county to be the "courthouse."

Deputies swept both buildings for signs of the devices and then took individual staff members through their work stations to determine if there was anything out of place, but no evidence that the threat was material was discovered, Fitzgerald said.

At 9:30 a.m., the justice center was reopened.

Fitzgerald said the Story County Jail, which also is in the facility, was not evacuated because it, like the dispatch center and sheriff's offices, is a secure facility with restricted access. Instead, he said, prisoners were put on lockdown for the duration of the event.

Fitzgerald said investigators are working on tracing back the original location of the bomb threat call and the investigation is ongoing.