What I have noticed in the book is that there are varying opinions about the morality of the murder. Perhaps the funniest for me is the sympathetic Dr Haydock who doesn't think to badly of whoever killed Colonel Protheroe, until the killer strikes again, this time choosing a victim who is much nicer than Colonel Protheroe. Apparently your opinion of the victim can influence your opinion of the murderer.
And then of course there is Miss Marple. My opinion of her changed throughout the book. I started off not being sure I liked her - she wasn't what I imagined Miss Marple to be like. That's the curse of watching an adaptation of the book before actually reading it. But my opinion is changing.