Honestly, the reason I thought Kai might be Pisco in the first place was because you guys killed off both Jecka and Kamite early on, making me wonder if you guys killed them so you wouldn't have to tie up the BS for a fake action if they happened to try to ally with her. (I forgot about Pisco having accompany and thus possibly being able to pass as Haibara/Kazuha, mind you.
Maybe I did guess Raiden was BO even before Yuriko died, though... At the very least, I had a feeling that if I told him who I was healing, the BO would somehow find out and thus make me utterly useless. XD (I think that was the same phase I healed him, too... The BO would've had a field day with that.