I think he is, initially he is in denial and he doesn't buy it for a second but he is crashed about the news anyway so part of him believes it if he has that reaction, evidence is pretty strong, then he is just trying to find who killed her, in the end there's a ray of hope but...
As for me I'm not sure, it seems really off, that she'd go out like that even if Ruth is unavailable, it'd be really lazy and convenient to end her story like this off screen, and kinda insulting to send off a great character like that, and like I said