You are one brave young woman to face the man that brutally murdered your mother. Of course having Dr. Phil for a bouncer helps a bit. But what's important here that you understand that the power in forgiveness lies in the heart of the forgiver and not in the forgiven. You are not releasing him from his pain. That's his job. You are releasing you from your pain, and that's what's most important.
As for a relationship with your father, please don't give up on yourself or even on him. People change and I know from whence I speak. I divorced my children's mother and left my family when they were young and they grew up learning to hate me probably as intensely as you did your father. But after some encounters as intense as yours was and by utilizing the teachings of Dr. Phil, we are doing much better now. By my own following of the teachings of Dr. Phil I learned what it meant to be a man and own your mistakes. And because of that, I've received the gift of having a second chance with my children, and now my grandchildren. I didn't kill anybody like your father did, but I did the next best thing by causing my daughters to believe that they didn't count and crushing their spirit. I'm not the same man that left them and their mother over 20 years ago. And your father may very well no longer be the man that brutally murdered your mother.
So please Erica, from a humble and grateful father who was given a second chance by his two daughters, I beg you please don't give up on your father. He is deeply sorry and regrets what he did as much as anyone walking this Earth. He just may need a little more time to discover a way to express that to the world that is outside of his heart. If he means what he says about staying clean and sober, his behavior will demonstrate that. If you really want him to mean what he says like you stated you did, please allow his behavior to demonstrate that to you. That's what will tell you he's sincere, not what his mouth says.