Very disturbing and glad you were able to escape his abuse. A couple of thoughts: if you try to expose him anonymously, I am going to guess he is going to be able to know who the source is. Are you sufficiently protected against him if he does find out? If not, you have to think very carefully what/how to proceed.

Are you part of any support groups? sharing with others can be very cathartic and through their support and suggestions you may find ways of protecting others from his abuse.

Sorry I don't have more concrete suggestions.

Power to you!