I don't think killing Nin to find out what is up with the book is a good idea. Unless he is actually a cultist, which seems unlikely given that he volunteered info about it (which has now been confirmed) and put himself on the spot, it will go pretty bad for us.
If he is a Tourist it tells us nothing. Future holders could still be cult. If he's an insane tourist (suggesting that the book is going to the pre-insane people) the Cult can get a free recruit on NeverForever tonight, which would be extremely bad.
One thing I found interesting from LoC's posts is that he had Lone_Prodigy listed as a "our best D1 choice.":
http://www.neogaf.com/forum/showthread.php?p=174497937&highlight=#post174497937 That suggests to me that bussing L_P was a strategy on the Cult's minds extremely early in the game. Seems possible his reactionary posting style made the cult make the decision to cut him loose very early on as a way to give them some early credibility.