In my WHAT IF world I will tell you how we would know. An infector (selfish greedy wantonly promiscuous babybrain) would have the word MURDERER appear on his/her forehead. Then on both arms. Then on both legs. MURDERER MURDERER MURDERER MURDERER MURDERER. That's how we'd know. Such vermin maggot roaches would be charged tried convicted and spend the rest of their lives in prison. A perfect solution to execution. You murder you die. No t'wixt and no t'ween. You want YOUR right to live your life as you please? You LOSE that right when you murder others. Simple. AN EYE FOR AN EYE except you don't die quickly and easily. You linger for years suffering. A small way to pay you back for all your selfish acts. In another world on a different plane in my imagination. Only fair.