Coercion is a legal defense. If someone is holding a hostage and orders you to rob a store that is a valid defense, however you have to prove the defense not just raise doubt about the DA's case. So to defend about the robbery he'd have to reveal who was being held which causes problems.
How early it happens would also matter I'd think, after several years of Superman there would be lots of people that would either think it was a trick to discredit Superman or that he had a good reason.
