Its an interesting twist but kind of a big nonsense that a lil girl would be able to commit such crimes without making any mistakes along the way. Well, this isnt the type of series we should bother about logic i suppose.
Tho i imagined from the constant focus on Rinko empty eyes that something was up mostly with Kuroko constantly noticing it. But the timing seemed odd. Like, didnt she recently saw the video from her father? She would already had been killing for a long while before the video.