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You may file a complaint with the governing board for your church at the most local level directly above the church if you wish to try to resolve the matter without going to the police. This assumes that your church is part of a denomination that has such a governance structure. If your church is non-denominational, you would have to meet with the pastor, confront him with the allegations, and ask that he resign and return the money to the congregation.
Otherwise, you are going to need to file charges with the appropriate law enforcement agency in your area so that it may investigate the matter.
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