Instead of just saying that he is not responsible for what happened, you could ask, “What makes you think that it is your fault? ”
في هذه الحال ،‏ لا تكتفِ ان تنفي ذلك بل اسأله مثلا :‏ « لمَ تعتقد ان الحق عليك ؟‏ » .‏