The professor who is accused of killing three colleagues at the University of Alabama on Friday was a suspect in the attempted mail bombing of a Harvard Medical School professor in 1993, a law enforcement official said today. Bishop surfaced as a suspect because she was allegedly concerned that she was going to receive a negative evaluation from Rosenberg on her doctorate work, the official said. The official said investigators believed she had a motive to target Rosenberg and were concerned that she had a history of violence, given that she had shot her brother to death in 1986.