As a joke, the two 19-year-olds billed their New Year's Eve party in an Internet invitation to friends as Night of Mayhem. Later, of course, that didn't seem so funny. The evening in a three-story Edwardian home in San Francisco's Richmond District began as a gathering of college kids who had graduated from one of the city's oldest private high schools, St. Ignatius College Preparatory. Guests of honor were members of the Baker's Dozen, an all-male a cappella group from Yale College that was in the city on a tour. The night ended with one member of the Baker's Dozen...