I actually read that book, because I was stuck somewhere one night with not a whole lot else to do. I learned a couple of things, but overall the book rubbed me the wrong way. It was superficial and focused on the least interesting parts of the assassination. And making a goddamn series of "investigative journalism" about the deaths of US presidents is crass. I am not surprised that the details aren't entirely consistent.
I don't know if anyone else on hubski really bothered to read it, so I'd figured I'd share my experience.