Mystery novel where the first person point of view is of the killer?

Well, a good idea but it has been done both in books and in movies. I read about 4 to 6 books a month and I apologize that I cannot provide you with the titles and authors of examples. One movie that slightly fits is "Double Indemnity" 1944, although I know there are other better examples. This does not mean that you should not try to take the approach but it might help you to read some other work written in this perspective.