There would be an evidentiary hearing, not an appeal. It would likely work as follows:
1 - James comes forward, says that he's the one who killed Pratt; 2 - The US Attorney (the prosecutor) would assess the credibility of the evidence; 3 - The defense (Peter's attorney) would argue that the evidence is credible and exonerates her client; 4 - If the US Attorney doesn't challenge the evidence, there would be a motion made by the defense to dismiss the case; 5 - If the US Attorney wants to challenge the confession, there would be an evidentiary hearing and the judge would rule on the credibility; 6 - If the judge finds the evidence credible, then either the charges would be dismissed (if the case hadn't gone to the jury) or the conviction overturned (if Peter had been found guilty).
no subject
1 - James comes forward, says that he's the one who killed Pratt;
2 - The US Attorney (the prosecutor) would assess the credibility of the evidence;
3 - The defense (Peter's attorney) would argue that the evidence is credible and exonerates her client;
4 - If the US Attorney doesn't challenge the evidence, there would be a motion made by the defense to dismiss the case;
5 - If the US Attorney wants to challenge the confession, there would be an evidentiary hearing and the judge would rule on the credibility;
6 - If the judge finds the evidence credible, then either the charges would be dismissed (if the case hadn't gone to the jury) or the conviction overturned (if Peter had been found guilty).
No need for a new trial.