For some reason your story made me think about my brother-in-law. He was a kind, stable loving husband. Then when he and his wife had a baby, he developed some very serious mental health problems and basically abandoned his wife and child. Something about the baby/fatherhood/family (not sure exactly which; maybe all) triggered serious drastic changes in his personality and upset the balance of his mental health. They weren't a young couple at the time -- probably mid to late 20's at the time, so it wasn't an issue of being too young for them.

His behavior became unpredictable and unreliable, not like the person we all thought we knew. His wife tried to deal with the changes, but when the baby showed clear signs of being afraid of her father because of his generally odd behavior (he was not violent), his wife filed for divorce and moved on. Something very deep had changed in him, and he never did "come back". My brother-in-law never did make any effort to re-enter his daughter's life, and we never did gain any solid understanding of what went so terribly wrong.

You mentioned him being "dead behind the eyes" which I think is what got me to thinking about this. Something has clearly changed in him that you or your family or from the sounds of it even his own family doesn't understand. Unfortunately, you probably can't save him; we have no power to change others. Do what you can to move on and make your daughter's life as blessed as you can. She is most important here. Demand his financial support. Insist that he get some help so that maybe he can be a meaningful part of his daughter's life.