The trial must be a win otherwise we lose our right to self defense or at least it will be eroded. Also if the mob is allowed to win again like they did with Chavin it will give them more incentive to do it to whomever they like. The mob must lose and an example must be made.
It would show that mobs can be used as a weapon to try and control the outcome of a trial.
Imo it's about controlling the mob that will riot and attack if they don't get their way. It's about their ability to twist the truth and control people to do their bidding.
Perhaps they are controlling their mobs like this so in the future when they themselves are on trial they could have the mobs persuade the judges to rule in their favor.