Who is the protagonist in I'll Be Gone in the Dark by Michelle McNamara?

As a true crime book and an investigative piece looking into the murders of the Golden State Killer in California, the main protagonist is the author Michelle McNamara. As she states in the book "I've written about hundred of unsolved crimes . . . The Golden State Killer, though, had consumed me the most."
In the prologue to the book, McNamara states the Golden State Killer (also known as the East Area Rapist and the Original Nightstalker) was responsible for ten murders in southern California and fifty sexual assaults in northern California from 1977 to 2018.
Through interviews with victims and police officers and through retellings of the some of the killer's most brutal crimes, she reopens the case and does a lot of the groundwork that led to the killer's eventual arrest in 2018. It was just unfortunate that she died only months before his capture.