Here is Pruss’s argument:
1.Even if God didn’t forbid it, torturing the innocent would be wrong.
2.(Premise) Necessarily, torturing the innocent is wrong.
3.(Premise) Possibly, God does not forbid torturing the innocent.
4.(Premise) If divine command theory is true, then it is the case that: necessarily, something is wrong if and only if it is forbidden by God.
5.Therefore, divine command theory is not true.