sorry, but from what you have said, I think this child does have problems of some sort.
As hercules says " I would be cross, I would speak to the school but I would not say a child who clearly has problems is a shit. There are lots of children who come from great homes who still have problems. They need support as does the family. Personally I think it is a sad world when a child with problems is called evil."
kimi, I know you say you have friends who have special needs children and you say this boy is definitely different, but how can you be 100% sure?
I'd certainly be cross if my sons were being attacked like this, but really think your anger should be directed towards the school. As it stands, the school holds the only possiblity of change for the better. The son can't, the mother won't, but the school can do something.
My oldest son was bullied last year and it is still continueing. I have written a letter, met the teacher (took my son along as well) keep tabs on what's happening, but decided a long time ago that direct confrontation with the parents or child was a no no. The boy can be very supercilious to me as well as to my son, and it really winds me up. At a party, he taunted and hit my son right in front of me. My son started hitting back, I told off both boys, got the help of another parent in breaking them up (couldn't manage to physically separate two strapping 9 year olds by myself) and the mother just stood around at a distance smiling away. I could feel the anger welling up. I just decided it would do no good to confront right then as I was so cross. The boy's parents are both active in cubs and PTA events, so do care, but for whatever reason, don't seem to intervene. I know they have had to see the head several times with their son, so assume there is a problem of some sort. To my outsider's eye, he doesn't appear special needs, and gets no extra help in the classroom to mark him out. Perhaps he is being assessed and this will happen in time. I don't expect the parents to tell me. I feel I still have a right to be angry, but feel there's no point me directing my anger at them.
Now if your school are doing nothing - you say even this boy's mother has problems with the senco, then perhaps you should move your son away. I sympathise a lot. It is not fair. It's a drastic step I know, but it the school is S* then that IMO is your ultimate solution.