If you knew the civilian criminal justice system was corrupt, would you use that system if you could prosecute high-level crimes in another court system?
If you knew government department heads conspired to overthrow a duly elected President and you intended to bring charges of treason against the perpetrators, would you hold the trials in a civilian court or a military one?
Every totalitarian system always has an elite oligarchy, at the top that exist under their own set of laws.