T.R.
Well I am not sure if this will be any help but our neighbor had a biter and he would come to play with our son. More than once he bit him, once even on the back of the head! I had to put my foot down about him coming over if this did not stop. So when he tried to bite him the next time he was removed from the house and not allowed over for several days. After removing him from the situation several times he stopped doing it. What I found is that anytime there was something going on in their house, fighting, etc he would start biting. I think it was the stress or something. Maybe some situation in the house is setting him off.
T.