Mysscat- not trying to avoid your question, but what a hard question and decision at that. What does your heart tell you? Mothers instinct is usually right on.
I personally would not write back. It might be wrong, but I couldn't give comfort to someone who had hurt my child so badly. Neither would I write to berate him - wouldn't waste the time. If he is a sociopath, he feels no remorse and is probably trying to play the system by looking contrite. If not, he has to realize that he must pay for his action. Let him serve his full term. That will keep the streets safer for the rest of us.