If a Mufti has got knowledge of a crime must he report it to the authorities?

Many people consult scholars for asking questions, sometimes they even reveal their own misdeeds to these scholars in order to get a fatwa or solution to get back on the right path. My question is if a questioner revealed a crime zina, killing, robbery etc. must the mufti report this questioner to the authorities? Or can he conceal this information? What is the correct ruling on this (For example.: in what cases is it allowed to conceal and when reporting is obligatory)?