You son will need to pursue his appellate options. He and his attorney will want to challenge the validity of the trial and examine the record closely for rulings made by the court that can be challenged. Basically and appeal gives you the ability to get a new trial for 1) bad evidentiary rulings, 2) errors so significant that the trial was tainted (plain error), and 3) insufficient evidence as a matter of law (very hard to win on this).
If the appeals fail then your son may wish to challenge the validity of the trial because of some deficient performance of his attorney. This is called ineffective assistance of counsel. Generally we see these challenges filed after the final appeal is completed in the form of a petition for post conviction relief. Ineffective assistance of counsel claims are hard to make as you must show the attorney's representation was so ineffective as to render the trial unconstitutionally unfair. This is a very hard standard to meet.
If that fails then he will be basically limited to writs of habeas corpus (unlawful paperwork or procedure was used to hold someone captive) or a writ of error coram nobis (a writ filed if new evidence that would clear a defendant is discovered post trial). These writs are rarely granted and seldom given any attention by the courts.
To answer your specific question about the facts of the case... the trial is designed to sort out facts in a case. Apparently the jury did not believe your son's claims that he was held under distress. Juries are the judges of the facts in a criminal case. While appellate courts give the jury a great deal of deference, if your son's attorney can show the record does not contain sufficient proof to convict him then he could be granted a new trial. The standard requires the court view all facts taken in a light most favorable to the prosecution. Using this standard, if there is still insufficient evidence to support the verdict then it cannot stand.
His attorney will need to guide you through the elements of the offense and where in the record the state proved his guilt on each element.
Please reply if I can help further.
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