I just had a thought.
I think I know Itachi why did not kill Orochimaru when he could have back when the latter tried to steal the former's body.
Could it be because he knew Orochimaru would leave Akatsuki after that, then become an enemy of Akatsuki? That he knew Orochimaru's potential as an enemy of Akatsuki?
Orochimaru is not dumb, and he is not weak. Orochimaru is a Sannin. And he proved to be a hated enemy of Akatsuki.
Dat Itachi Lol