If exculpatory evidence—evidence that tends to prove innocence—is discovered after a court-martial verdict of guilty, the accused has the right to petition for a new trial. This is a critical post-trial right designed to prevent a miscarriage of justice. The process is governed by the Rules for Courts-Martial and the UCMJ. The discovery of new, significant evidence is one of the few ways to challenge a conviction after the trial has concluded.
To be successful, the petition for a new trial must meet a two-pronged test. First, the evidence must be “newly discovered.” This means that the accused and their defense counsel did not know about the evidence at the time of the trial and could not have discovered it with reasonable diligence. Second, the new evidence must be “material,” meaning that if it had been presented to the original court-martial panel, it would have likely produced a substantially more favorable result for the accused.
The appellate defense attorney will file the petition with the Judge Advocate General of the service or the appellate court reviewing the case. The petition will present the newly discovered evidence and will make a detailed legal argument explaining how it meets the two-pronged test. If the appellate court agrees that the new evidence is significant and could have changed the outcome, they have the authority to set aside the conviction and sentence and to authorize a completely new trial where the new evidence can be presented.