I think he started with online available info (I believe Reddit has a good identity theft community), but the thing is that notices keep coming long after fraud has been committed. So every week he would find out there are more things he was on the hook for.

Eventually he hired a lawyer to help him out, there are so many reporting agencies (for subprime loans etc) that you need to reach out to.

Long term a new SSN will be issued for him, but there is a lot of cleanup before that.