Recalling the 1955 murder of a 14-year-old black youth in the Mississippi delta, an incident that could very well have launched the civil-rights movement. "He was a sacrificial lamb," says Mamie Till of her son Emmett, a fun-loving Chicago teen who was slain after whistling at a white woman outside a general store in Tallahatchee County, Miss. Less than a month after Till's mutilated body was found, two white defendants were acquitted (in 67 minutes) by an all-white jury.