SAN DIEGO -- A former University of California, San Diego employee pleaded guilty in federal court Tuesday to making bogus threats to blow up buildings on campus if research animals weren't released.

Richard Sills, 54, faces up to five years in prison when he is sentenced June 16 by U.S. District Judge Larry Burns.

Sills pleaded guilty to one count of making threats involving animal enterprises.

The Encinitas resident, a temporary employee in the UCSD Biomedical Science Building, admitted making two phone calls and sending a letter to the university claiming there was a bomb on the campus on Dec. 5.

According to an 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 had placed remote-controlled explosive devices in six campus buildings, and the devices would be detonated unless animals from campus research facilities were released, according to the indictment.

A bogus device was found the morning of Dec. 5 at the Leichtag Family Foundation Biomedical Research Building.

Another man who had recently been fired from the university, Timothy Kalka, was originally arrested in the bomb hoax, but charges against him were dismissed.

Sills entered his plea Tuesday in a hearing before Magistrate Judge Louisa Porter. The defendant will have to pay $10,419 to his victims, including UCSD.