My understanding (and legal experts on here may know more) is that a treason charge is a particularly difficult one to prove at the best of times. I believe the onus of proof is particularly high.
That is "presumed innocent until proven guilty". It's legalese and has nothing to do with anyone's opinion except those on the jury. OJ is guilty even though not convicted. Soldiers who were stationed with him have come forward and said he told them he was leaving. E-mails to his father indicated his disillusion. His actions of sending his personal effects home indicate something. Leaving a note indicating he was heading out say he was a deserter. Asking villagers directions to the Taliban is a red flag. I do not presume him to be innocent even if he says he is.