McNamara is a true crime writer and the author of I’ll Be Gone in the Dark. McNamara appears as a character throughout I’ll Be Gone in the Dark, with memoir-style sections describing her life and pursuit of the Golden State Killer. McNamara was raised in Oak Park, a suburb of Chicago, as the youngest in a family of six. Growing up, McNamara has a combative relationship with her mother and often rebels against her, leading the two to fight frequently. At a young age, a neighbor’s unsolved murder sparks McNamara’s interest in unsolved crimes. The murder haunts McNamara, particularly the unknown identity of the killer, leading her to develop a deep interest in serial killers.

Over time, McNamara becomes an amateur sleuth, using the internet to investigate unsolved murders. She writes about her investigations in a blog, True Crime Diary, where she gains a large following for her true crime writing. McNamara first learns about the GSK in a book, Sudden Terror, written by a former detective. Her obsession with the case leads her to an online forum where members share possible evidence and debate theories as to who the GSK might be. McNamara grows obsessed with tracking down the GSK, spending her evenings combing evidence for possible leads.