You don't have to feel guilty about it. Death is the fate of every living being, and from the moment we are born, it is the only certainty we have in this world. If you never wanted it and never did anything against it, you don't have to feel guilty or have a guilty conscience. I am sure that when he came to you to offer help, he did so with the belief that he could do it. He knew better than anyone what he was exposing himself to. I say this in case that is what you think happened, but even so, it is not your fault.