nineteen-year-old Robert John Bardo was mesmerized by the flickering images on the screen and the hushed, sexy dialogue between the characters. That night, in a Tucson, Arizona movie theater, he was watching actress Rebecca Shaeffer being seduced right before his eyes in the film "Scenes from the Class Struggle in Beverly Hills." Bardo became enraged. The reason? This wasn't just Rebecca Shaeffer, the actress he'd written to repeatedly for two years and tried, unsuccessfully, to meet at Warner Brothers Studios. This was the innocent Rebecca Shaeffer he'd watched hundreds, perhaps thousands, of times on homemade videotapes of "My Sister Sam," the CBS sitcom on which she starred. This was …