A person who has pleaded guilty can't get the plea changed because he finds out that, had he fought the case, he would have been acquitted! As I have said before on AB, I once had a case, prosecuting,where a man pleaded guilty when I could not have proved the case in a month of Sundays, because the prosecution couldn't find the witnesses by the time of the hearing. He could not have changed his plea, and neither can the defendant here. The plea is final. It is a total admission of guilt of the offence and needs no more proof of guilt than that, though the details of the offence may be in dispute, hence the Newton hearing.