I reckon he's definitely involved in some way, whether or not he's been turned. But the preview for the next episode kind of ruined it for me, cause after watching it I felt there was no way that he did pass the razorblade.
Someone else guessed that Saul's the one that's been turned and is holding Carrie back to cover his tracks.
That's actually started to cross my mind.
Scene between Saul and Carrie at his house was intense.