FOUR UNSOLVED MURDERS In 1959, The Walker family murders shook Florida. At one time, 587 people were considered suspects - but 60 years later the investigation remains unsolved. AN FBI AGENT'S FINAL JOB Former FBI agent Brigid Quinn is trying to enjoy life after work. But when the intriguingly complex Walker case comes up, she's only too happy to postpone retirement for a little longer. A LONG-FORGOTTEN KILLER At first, Quinn is reluctant to draw comparisons with another high-profile investigation of the time: the Clutter family murders, made infamous in Capote's In Cold Blood. But the similarities are impossible to ignore, and she is convinced that Perry Smith and Dick Hickok, executed at the time, weren't acting alone - in both cases . . .