Well, he did say he didn't want to do anything about it for the sake of the children, so that doesn't sound like revenge being the most important motivator... I can imagine that sort of thing is a fairly complex ethical situation. Someone who has (for example) murdered someone or trafficked drugs isn't necessarily a threat to their own children, so the OP might be in a position where he's forced to choose the lesser of two evils etc. Anyway, this is all highly speculative and the reality is we don't know anything about the situation really, or even whether it's actually all true. Probably better off giving legal advice rather than moral advice.