He’s literally able to deduce that Yotsuba Kira is not the original Kira (himself) because the original Kira (himself) did take circumstances into consideration and would show mercy and the other Kira did not.

Yeah, he showed mercy towards non-criminals, but as soon as someone was marked as a criminal he threw that all out the window

Ok, I mean if you’re getting financially screwed by your partner in a divorce, it’s probably a good thing that you’re getting divorced.