Of course the hand on Oswald's shoulder is there to reassure him. It is also there so he could have the knife at his throat as quickly as possible, should Oswald attack him. Which at this point seems to be the foregone conclusion to draw, given his overall behaviour. Edward is already thinking past that, who was it that poisoned Oswald against him? What goal do they have in mind and what lies did they use? He isn't planning on killing Oswald, so he'll just have to convince him right after subduing him.

For now he smiles a tight smile, ready for whatever Oswald might attack him with. Hopefully. "Is there? Here I know so much already." He pauses for a moment, lips pressing together before he smiles again. "What is it?"