User blog comment:GinIchimaru/The Zero Squad: Reality vs Speculation?/@comment-1774413-20100413152654

I really doubt whether Isshin was in the zero squad. My reason is due to something Aizen said, Aien said he knew about ichigo since he was born, to me this indicates he knew of Isshin and his relationship with masaki. However had isshin been in the zero squad there is noway Aizen couldve known about him or who he was (as he only learned about the existence of the squad in the Tbtp story)... thus he wouldnt have known to watch his relationship with masaki for future offspring.