With a title like that, I have to wonder if the author saw the same video as me. Clearly, there were two robbers, and the policeman neutralized the one with the gun. I don’t think what he did was excessive at all. The armed robber had a gun in his hand and the policeman acted first in a busy intersection. I don’t know why you would call that “no mercy”. It’s not as if he kept shooting the robber after he took the gun away from him.