Consider a society with regularly scheduled, periodic anarchy. Perhaps a day, once every few years, there are no punishments for crimes committed.
Crimes are still tried in court, but no punishment is handed out. The justice system seeks the truth.
The other reason for seemingly pointless trials is because the anarchy is periodic. The state might not punish, but in the next iteration of anarchy, vigilantes have concrete justification for revenge.
The ultimate goal is to level the highly unequal power structures that develop over time, though I am skeptical that this will work.
The tree of liberty must be refreshed from time to time with the blood of patriots and tyrants.