The machine-gun murders of seven men on the morning of February 14, 1929, by killers dressed as cops became the gangland "crime of the century." Or so the story went. Since then it has been featured in countless histories, biographies, movies, and television specials. 'The St. Valentine's Day Massacre,' however, is the first book-length treatment of the subject, and it challenges the commonly held assumption that Al Capone ordered the slayings to gain supremacy in the Chicago underworld.