Thank you , everyone, your support is really something to me, all of you give me good suggestions, I understand, the bottom line is that I should avoid doing anything that may hurt me later again, hope it doesn't mean that I cannot do anything. I really don't want to get any rewards from this , and I'm NEVER a person to punish for punishment or make any dirty deal. To my wife (so far) , except to divorce (maybe it's even not a punishment in her eye, I guess, she is expecting her new life), I won't do anything else harmful to her because she is atleast my kid's mother, and I believe that my kid won't be happy to see his mother is in any trouble. But, that guy have to pay back what he did, because, If I don't do anything, that means, immortal person enjoy life, moral person suffers hurt, and I tolerate that my kid's life and happiness is ruined by others' evil helplessly, that's not me. so, when the law is not able to help me on this due to some reason, I need do it by myslf, for myself and for my kid. Sometimes, I can really understand the helpless feeling of those peoples who kill others, although their action is cruel and I don't agree with them, that's why I come here for suggestions, because I even don't want to do anything illegal. As to evidence, because I'm working long time all day, it's impossible for me to get it, and those dirty details are not my interest either. If I can only wait now, I will.

BTW: What ONS means?