What would you do in this scenario (hypothetical)?

I came across this question on a website. It is very intriguing. What would you do? Why?

A Father’s (or any parent) Agonizing Choice

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. He says that if you don’t 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?

Would your opinion change given more details? If the other prisoner was a child, a pregnant woman, an elderly man. If your son was already terminally ill. in fairness I edited to add this bit