Your assuming that the trial would be run on Western lines. In the Avatar world, that might not be a guarantee. To me, the trial had some similarities to how a trial would have been held in Imperial China. I know the water civilization is more Inuit than Chinese, but the Earth Kingdom is sort of China in this world, and in the Korra world of cultural exchange, Earth Kingdom legal procedures could have become the norm (as the kingdoms with the best established beurocracies one would assume either Earth or Fire or a mix would dominate) And there IS some evidence that the writers of Avatar are familiar with Chinese legal proceedings (the winged hat Sokka put on when he was playing "Sherlock Holmes" on Kyoshi Island is a Chinese Magistrate's cap. ) In those, the "judge" IS the prosecutor (at least, for criminal cases and treason is a criminal charge) since he is the local magistrate (he's also the chief investigator, which is why Sokka refers to his hat as a "detective hat"). There IS no jury; honesty and accuracy is supposed to be enforced by fear of punishment (under Imperial Chinese law, if someone knowingly brings criminal charges against another person that are proved false, the bringer of charges is subject to whatever punishment would have been meted out should the charges have been proven true. This also applies to the judge himself, if he judges wrong, he could face severe penalties). It isn't a perfect match. For one thing Korra's father and the others were sitting (in an Imperial Chinese trial, all participants are obligated to kneel on the floor in front of the Judge's dais) and were not obligated to sign confessions (just as well, since the judge is permitted to use torture to get confessions in the case of the recalcitrant) But the similarities were eerie. I'm not denying the trial was rigged, but it was not as OVERTLY rigged as it might appear to us
"For I have heard the Song of War, and to me, it sounds just like "Please, Mister Custer.""
Cogito Ergot Sum, "I think there is something wrong with this rye bread." (Aplogies to Seafrol.)