I still think he's a BO member. Here is my reasoning:
Just because he said he was a detective doesn't mean he is one. If he's Bourbon and he's a lot like Sherlock Holmes, then it wouldn't be a surprise that his deduction skills are amazing and that he would lie about his true identity. I mean, saying you're a detective is a great way of covering your tracks if your deductions skills are as good as his. And even if things start to look bleak for him being a BO member, maybe this will be something like with Vermouth when we were introduced to a real character (Araide), but it was actually Vermouth in disguise. Not to mention, he never had the box with his name and age and occupation in it (isn't that a bit suspicious?). Finally, he knew how to speak English. At the end of chapter 769 he said, "Case Closed." Sure, that might not mean anything, but I have a theory about the BO. I think they might have some connection with the western world. I mentioned this in another topic, but I'll say it again. If you think about it, almost every BO member has some sort of connection to the western world. Gin drives a Porsche 356A. Vermouth is American. Haibara is half British. The number one culprit for Anokata is Agasa who drives a yellow VW. Sera can speak English, and if in the future he shows even more English speaking ability, then he's a prime suspect for Bourbon. That's all I'm saying.