In a luxury Boston hotel on April 14, 2009, police discovered the body of a beautiful young woman-her head battered, a bullet through her heart. Within hours, the story exploded, making headlines across the nation. The victim, a masseuse named Julissa Brisman, had advertised her erotic services on popular classified ads Web site Craigslist. A twenty-two-year-old medical student named Philip Markoff was her last-known client...

The Boston Police Homicide Unit followed a digital trail that led to Markoff's home, where investigators found a gun, prepaid cell phones, plastic...