What are your ideas on my ideas of a book I want to write?

I want to write a book on either serial killers or just killers in general. I want to do a simple interview through mailing letters. First ask their permission, then ask the questions I'd like to ask. If they respond, they respond, if they don't, they don't. Then I will put the questions and their responses together along with facts, ideas, maybe my opinions. And make a book out of it.