It may sound odd, but in the US it's the same. An appeals court only looks at the decision of the lower court solely based on the evidence and testimony presented at the first trial, and decides whether there was any error of law, or whether the defendant's rights were denied or infringed, or whether the evidence PRESENTED AT THE TIME did not justify the court's decision . If the court were to find that exonerating evidence was withheld improperly, or that the defendant didn't receive adequate or lawfully competent representation, then a new trial can be ordered, or the conviction reversed. But the appeal doesn't RETRY the case. If it finds error, it will order a new one. In the US, a new trial can be requested separately from an appeal, based on NEW evidence, that is a different sort of action. I have absolutely NO IDEA as to Thai law in this regard.