I would not be surprised if he had chosen Nui, though the method doesn't fit if so. He didn't strike me as a man to have familiarity with firearms unless he is quite duplicitous or has been practicing.

[ What with the whole renaissance Italy thing and all... But the question makes Hannibal tilt his head lightly, since he's not sure if he understands. ]

The rest as in other murders? No. I believe he's only responsible for one.