I got a letter from the man who molested me as a child... what do I do?

A little back story... I was molested as a very young girl (age 4-6 or so) by my uncle who was in his late teens/early 20s. I remember the abuse in bits and pieces, since I was so young I don't remember every detail and I know at some point my dad found out and confronted my uncle (my dad's brother). The abuse stopped, but he was never punished and no one spoke of it again in my family. I spent many holidays and family gatherings in my uncle's presence growing up and had to pretend everything was fine.

I'm now in my 30s and my uncle sent me a friend request on facebook a couple weeks ago. I was more than a little angered by it, thinking he was pretty arrogant to think I would want to be friends with him. I thought about just ignoring it, but I felt like I didn't want to let him get away with being such a prick yet again. So I sent him a message telling him I wouldn't be his friend and that I hadn't forgotten what he did to me when I was little. Last week, I got a response back with a long letter attached basically saying he was sorry for what he did to me and explaining that he had been molested as a child and he was in a really bad place when he did it to me. He claims he was on drugs at the time and that once my dad confronted him, he realized he had become a monster and he never did anything like that since. I can't really believe that, but I'd like to, since I have felt guilt all my life about letting him get away with it.

Now that the dialogue is finally open after all these years, I have so many questions I want answered about things I only half-way remember and so many things I want to say to him about how what he did affected me. But I'm not sure if I should even respond. I'm hoping I can get some help from fellow redditors. What do I do? Should I respond and try to find out answers to all the burning questions I have, or would that just give him the satisfaction of knowing he can still get to me? What would you do in my situation?

EDIT: I just looked up the current statute of limitations in the state where it happened (and where he currently resides) and it is 9 years.
We are way past that.

EDIT: I want to thank everyone for all the insightful responses and advice. I think the one thing that is clear to me is that I need to focus on healing and he really can't be a part of that. I still don't know if I'll respond to his letter, but I have as much time as I need to figure that out.