SAN DIEGO -- A former temporary worker at the University of California, San Diego, who made bogus threats to blow up buildings on campus if research animals weren't released, was sentenced Monday to 15 months in federal prison and ordered to pay $10,419 in restitution.

Richard Sills, who pleaded guilty March 11 to one count of making threats involving animal enterprises, was sentenced by U.S. District Judge Larry Burns.

The 55-year-old La Jolla resident admitted making two phone calls and sending a letter to the university claiming there was a bomb on campus last Dec. 5. A bogus device was found that morning at the Leichtag Family Foundation Biomedical Research Building, where Sills was a temporary employee at the time.

According to the indictment, Sills said in the second call, "Take this very seriously. There is a bomb in the Leichtag Building. Take this very seriously."

Sills also sent a letter to the UCSD Police Department stating that the Animal Liberation Front would detonate remote-controlled explosive devices the activist group had placed in six campus buildings unless animals from campus research facilities were released, according to court papers.

Assistant U.S. Attorney Peter Mazza said Sills' sentence was on the low end of the agreed-upon federal sentencing guidelines because it did not appear he was affiliated with the Animal Liberation Front.

"It (the bomb threat) was his form of expression against testing on animals," the prosecutor said.