Agonizing choice

A Father's Agonizing Choice (friesian.com) You are an inmate in a concentration camp. A sadistic guard is about to hang your son who tried to escape and wants you to pull the chair from underneath him. The Ethical Dilemma: He says that if you do not, he will not only kill your son but some other innocent inmate as well. You don't have any doubt that he means what he says. What should you do?