About 500 people crowded Saturday into the plaza where John F. Kennedy was shot 45 years ago, all agreeing it was right to remember a pivotal moment in American history, even if they didn't all believe the official line. People stood shoulder to shoulder and bowed their heads during a moment of silence at 12:30 p.m. Some hawked JFK memorabilia or pitched conspiracy theories to visitors. Others offered firsthand accounts of their memories of the killing.