Five buildings were evacuated Tuesday after the e-mails began surfacing, but the threat turned out to be false and no hostages were taken, FBI agent Tim Fuhrman said.

William Stiffler, 39, was unarmed when he was arrested Tuesday in Malad, Idaho, as he prepared to board an employee shuttle to the base, Fuhrman said.

Stiffler has worked on C-130 planes at Hill since 2001. He was arrested for investigation of making threatening communications through the Internet and was expected to appear Wednesday in federal court in Salt Lake City.

Fuhrman said FBI headquarters received an e-mail from Stiffler about 12:30 a.m. Tuesday, followed by another with similar content three hours later. He said the six people who were to be taken hostage according to the e-mails were found unharmed; each had a connection to Stiffler but were not affiliated with the base.

Stiffler didn't identify himself in the e-mails, but Fuhrman said the FBI was familiar with him. He did not elaborate on why.

Linda Medler, vice commander of the 75th Air Base Wing, said all 24,000 employees at the base undergo a background check. It was unclear if Stiffler has a criminal record.

''This one was pretty unexpected," Medler said.