interesting timing of this post. Just yesterday I was thinking about buying Monster manga. 9 books about a genius serial killer. I already own in my opinion the best fantasy books Berserk so I would like to have the pinnacle of thriller as well. Right now Monster books are especially tempting because they are on a discount. Also I fear that it might go out of print again. Still for now I resisted the urge to buy. I am a bit spoiled by Berserk manga because it has both a magnificent story and unbelievable art. Monster has great story but visually it is not as good as Berserk( almost nothing is as good). Also I may need that money to buy Hive if the price will drop much more...
I don't know much about manga, but supposedly, the trick to writing a genius character, is to write it backwards. Start with the kill, and then build all the tricks to get there after.