The only son of President John F. Kennedy, John F. Kennedy Jr. always lived in the media spotlight. On his third birthday, ''John-John'' attended the funeral of his assassinated father and was photographed saluting his father's coffin in a famous and searing image. When he grew up, he was named the ''Sexiest Man Alive'' by ''People'' magazine and dated celebrities before settling down to marry Carolyn Bessette and run his moderately successfully political magazine, ''George''. Known for his adventurous nature, he nonetheless took pains to separate himself from the more self-destructive behavior of some of the other men in the Kennedy clan. On July 16, 1999, however, with limited flying experience, Kennedy took off from New Jersey with his wife and sister-in-law and flew his single-engine plane into a hazy, moonless night. He had turned down an offer by one of his flight instructors to accompany him, saying he ''wanted to do it alone.'' To reach his destination of Martha's Vineyard,...