11 year old hearing voices

I have an 11 year old with a diagnosis
of autism (since 18 mos). He is very high functioning, with the exception of socially. He has very explosive behaviors and can become aggressive. Recently he has been having difficulty with sleep, talking to himself and has informed us about the man in his brain who is telling him to do very violent things to us.
Several years ago he talked about monkeys in his brain telling him to do things, we sought the opinion of a psychiatrist who prescribed risperdol and diagnosed psychotic disorder nos.
The monkeys are gone and we are now dealing with a man in his brain and when I ask my son about this man, he said he has been there since birth. I am having trouble deciphering between the real possibility of schizophrenia or a very active imagination.
Here are my questions:
1.If this is true, how is it that my son can control when he listens and acts on the voices demands? For example, the voice tells him to kill and he doesn't do it, but the voice will tell him to call a girl a wh^^^ and he does do it.
2.Should I ask questions? if so, any ideas on what?
3.My son states that he wants to be good and thats why he doesnt listen to the voices. Is this possible?
Thank you in advance.