I'm still sticking to my guns about James Black being the boss. I really think he's suspicious. With his western relations and the fact that he's working with the FBI branch that investigates Vermouth, I find that he's probably keeping tabs on the FBI to make sure they don't get too far. I think he also managed to hide his "scent", knowing that someone (like Haibara) might start to suspect him. These are just my guesses. I mean, it's not like anyone else seems to be very suspicious. Like Agasa, for example. He's too friendly. James Black has always been a bit on the cold and silent side.