How is the author's voice present in The Strange Case of Dr. Jekyll and Mr. Hyde?

In this novel, there are several distinct voices that Stevenson uses to build up plot and move the story from start to finish. These voices can be seen as different parts of Stevenson’s overall voice for the novel. 
1.) Defining the undefinable. Most descriptions of Mr. Hyde, until the very end of the novel, touch on the theme that while he strikes other characters as disturbing to an extreme, it is difficult to put exact words to how or why. There are a number of examples of this throughout the story, and a good place to start is Mr. Enfield’s first conversation with Mr. Utterson. When Utterson asks, “What sort of man is [Hyde] to see?” (Stevenson 11), Enfield replies, “He is not easy to describe. There is something wrong with his appearance; something displeasing, something downright detestable. I never saw a man I so disliked, and yet I scarce know why” (Stevenson 11). (Note: this is a partial quote, and the rest is also relevant and worth a look.)
2.) Investigative. As Mr. Utterson becomes more deeply involved in figuring out the truth behind Dr. Jekyll’s strange behaviors, he begins to take on the voice of a detective. This comes out most clearly in certain parts of the dialogue.
For an example, see the conversations between Mr. Utterson and Poole that start in the chapter “The Last Night.”
3.) Self-Reflective. There are many letters in-text, as well as whole chapters, that come from a first-person perspective that not only relates past events but looks deeply into the thoughts and emotions felt by the given narrator. Often, these sections touch on complex themes and deeper overall meaning in more detail. See chapters such as “Dr. Lanyon’s Narrative” and “Henry Jekyll’s Full Statement of the Case.”