Investigation techniques described in this story are way behind what was available when this book was written i.e. in the late 1980s in the US. There is no mention in the novel of psychological profiling, a technique which really gloomed in the early 1970s under the leadership of the FBI and was widely used with success by the late 1980s.
In fact, it is difficult to imagine that an investigation of a series of over 10 savage murders (18 by the end of the book) would not have involved the FBI in any way or form, not even for technical advice.
The basic intrigue about two murderers, one copying the other, is not realistic. It is known in the police world that details of a murder scene are not revealed to media to prevent copycat. There are other inconsistencies in the story. Anyone who has read "Mind Hunter" by John Douglas and remembers some of it knows too much about police work to enjoy reading "Shadow Dancers".
Overall a very average read.