It has been long time coming, but the most inopportune time for him to realize/find out just after her mental state broke entirely and she regressed to a child. At least before that it would be easy to blame both her past life and her current equally, but now she's so pitiful that when she's coming at you with purely positive feelings it's kinda troubling to treat her as evil.
Though next chapter her mentality will probably somehow magically stabilize, so he can hate her again, and let her get executed (as if mangaka would allow that last part...)