We don't envy Linda Fairstein the 20-plus years she spent as the chief of the sex crimes unit in the Manhattan district attorney's office. We can only imagine the atrocities she must have seen during her time there. On the positive side, the experience has given her writing an authenticity and gravity that are hard to match. Fairstein signs and discusses her latest title, Death Angel, today at Murder by the Book. Angel follows Assistant DA Alex Cooper as she searches for a murderer who may have turned Central Park into his hunting ground.