Will I be investigated by the FBI for buying this book online?

No, I'm overly paranoid all the time like that too. But they won't. There are way too many people buying stuff like that online every second that they would never have the time to. Now, if you have a blog where you talk about actually doing stuff like him or how great he was, then yeah, they would probably look into that, lol. It's cool, what I do when I'm paranoid is come up with a legitamit excuse just in case I was being watched by someone. But you are allowed to buy whatever you want on the internet...except illegal stuff...because it's illegal.