Should we tell the committee about the imam’s sins? Is praying behind him haram?

Assalamu alaikum, Could you please advice as a matter of urgency on our. There have been rumours that he practices sihr with jinns. In the past he revealed to a person that he has a jinn with him and can help him with his troubled marriage. But instead of helping him, he visited his wife, while he was away and revealed his secrets and tried to marry her. She told him about his visit afterwards as she was shocked to see an imam do such thing. The imam also enquired about her wealth also. The imam also did sihr on a masjid committee member using jinn. His relations used a peer to find out as he kept falling ill. He has differences with the imam as he changed a lot of things in the masjid to help Allah S.W.Ts cause. i.e new carpet, new madrassa syllabus and new targets for madrassa teachers(imam are teachers also). There is evidence from 2 people regarding the imam also. Could you please tell me how do we go about informing the committee? Is it haram to tell them or is it our duty to disclose an imam who commits sins? Or we should keep quiet? Is it haram to pray behind such an imam? Jazakamullah kahirun