Between detective story and vision of a painstaking investigation

This book is not a thriller, here no suspense, no withholding of information (the real killer is introduced from the start), no narrative tension, the story is based on a real criminal investigation which we know the outcome, the killer had not been arrested at the time of the release of the book (there will be 2 years after the death of R Thorpe in 2001); and even if the final twist invents another end my review of this book remains mixed.
I found it strange to be guided properly investigated and remain in between, it oscillates between pure fiction and a semblance of reality and in my opinion the plot suffers.
The Boudreau's inability to prove anything for nearly 9 years of investigation then he knows who the killer is not very consistent. Besides the real killer of Green River had become a potential suspect in 1983 but due to lack of evidence and following a polygraph test misinterpreted it had not been arrested but was still left in the police who collimator would finalize it for at least 71 murders, 20 years after his first arrest, thanks to DNA evidence.
Reading this novel is not unpleasant but his writing density sometimes makes reading a bit laborious.
Personally I found it all a bit superficial: the investigation, the portrait of the serial killer, the attempts of the inspector and other representatives of law enforcement I have not really shuddered and I'm usually felt out of action.
No game of cat and mouse between the inspector and the killer: the interactions between the two men primarily limited to memories shared with the reader, among others, by rereading the notes taken by the inspector. The two characters meet this prevents any suspense or tension for the reader.
Here, reality is far more frightening than fiction: GL Rigdway, the real killer, was arrested and questioned several times for prostitution and of disappearances of women and relaxed, unlike his fictional character who escapes from prison that no one suspects apart Boudreau.
I still put 3 stars because I have not hated reading this book, he interested enough for me to read to the end, despite its 613 pages; I just wonder what the author wanted to accomplish and is a little on my hunger