Actually, the prosecutor in such a case would be the person saying God does exist, just as, in a criminal case, he would be saying “Yes, you are guilty”.
So again, Dawkins doesn’t have to prove there is no God. His opponents have to prove there is.
How so? Dawkins is claiming that those that believe in God are wrong. It’s up to him to prove it. As far as I can tell, he is the one that made the accusation against the believers. The believes did not single Dawkins out and charge him with being a non-believer.