On Monday, May 2, a year and a day after Shannan disappeared, Mari Gilbert and four other women came together in Manhattan to meet, at my invitation. Until that day, the five women had been in touch only through Facebook or by phone; just two of the five had seen one another in person. In addition to Mari, there was Megan Waterman’s mother, Lorraine Ela; Amber Costello’s sister, Kimberly Overstreet; Melissa Barthelemy’s mother, Lynn; and Maureen Brainard-Barnes’s sister, Melissa Cann. The group makes up a kind of grim sorority: They are the sisters and mothers of those who appear to have been the victims of the most skillful and accomplished serial killer in New York since Joel Rifkin or David Berkowitz, the “Son of Sam.”