A bomb threat on Friday was the seventh since February, and the 42-story Cathedral of Learning was evacuated for the fifth time.
Pitt spokesman Robert Hill says the school is determined to bring the person or persons responsible to justice. Hill says there hasn't been a similar wave of threats since he came to the school in 1999.
University police, the FBI and the U.S. Secret Service say they have a "person of interest" in the investigation.
Anyone with information about the threats is urged to contact the University of Pittsburgh Police Department.
