At the moment I'm just leaning towards him feeling the overwhelming guilt that would be associated with killing countless people. Mostly because if he actually sees what he's done, that might actually break his brain and I'm not 100 percent sure (yet) how I would play him if that happened.

Obviously, the guilt alone would either make him a) question or simply blame it on Edgeworth's abilities or b) make him start to second-guess himself, thinking back on L's suspicion directed towards him and wondering if it really is legitimate. Or both! Either way he probably wouldn't be very happy with Edgeworth afterwards.