In Galactic Republic law, a crime against civilization was the greatest crime of war one could be charged with. In a trial for crimes against civilization, the Galactic Senate would serve as the jury, with the Supreme Chancellor or the acting President of the Senate serving as the judge.
Ulic Qel-Droma was tried for crimes against civilization for his actions in the Great Sith War. During the Clone Wars, Kar Vastor was charged with crimes against civilization for his role in the Battle of Haruun Kal, but he apparently did not go to trial for reasons unknown. Depa Billaba was also supposed to be tried for the same reasons as Vastor, but she went into a coma, thus saving her from trial.