How you deal with them is to actually confront their behavior. It’s shameful that there are cases in which this hasn’t been done. 

Matthew 18:15-17 gives clear instructions on how to deal with a believer (or someone claiming to be one) who sins. There are far too many anecdotes of evil behavior being covered up to save face, or where monsters were even elevated to higher positions of power. None of this is the Way. 

It’s up to us to take loving action, protecting the vulnerable and teaching all to live in righteousness.