goal here is to play it cool and listen long enough that you can get to the truth.
try to reassure your child that he is not going to be punished. rather, your goal is to help him sort out what happened so you and he can determine what action to take. let him know that he is going to make mistakes at times, and it is important that he come to you or his dad to talk when he needs to in order to make a wrong situation right.
once you have a handle on what occurred, you can count on his conscience to help you figure out how to remedy 