⚠️ Spoilers ahead ⚠️
Personally, I like the books where you can't guess the killer till the author tells you. Those who are hating the book, I am seeing what all of you are trying to say, but i guess that's the whole point of the story. Mariana was so sure that Sebastian is the perfect guy and fosca is a murderer that she ignored everything which was right in front of her.
The book was not just a murder mystery, it's also coming out of a woman from a world that is made according to what she thinks and not what it truly is.