Before the invention of the justice machines, people had to use lawyers, juries, and judges to determine guilt or innocence. It was messy and unreliable.
Now, all you have to do is stand in a booth and wait for the machine to turn on a light.
Green if you’re innocent, and the doors open.
Red if you’re guilty, and the doors remain shut and sealed so the poison gas won’t leak out.
This wasn’t perfect either, so newer models don’t have the lights.
Too many guilty criminals were damaging the machines trying to escape when they saw the red light.