When crime becomes prolific enough, eventually it has to become organized.
Organized crime is never a force for good, but the amount of damage it does can vary. Not just by size of the operations but by management of the families. It happened that one particular city, not too long ago, had had a rather mismanaged underworld. Recently assassinations and bombings had shaken up the peace and the citizens could no longer live in peace. This gave impetus to vigilante justice of a strange nature.

The setting is a busy street in the center of the city. Regular lunch hours were over and people were returning to their desk jobs, it was the time of day where the pavement was visible and people had the room to walk around obstructions and clusters of people, but not so late that they had time to pay attention to these groups or obstructions.
The man gave a wry smile as he took a hold of the flask.
"Travelers from another world? I've decided to believe you, after what I've seen today."

He'd been wrestling away control of a fluorescent concoction from what seemed to be a group of regular teenagers. "Hand over the elixir, you villain." One of the girls proclaimed, with a regal bearing and tone, dissonant to her young body in its mature dignity.

In front of her stood an adult, a fully grown man easily half again her weight. Yet he was cautiously stepping back, increasing the distance between himself and the children. He was clean shaven and dressed in business casual attire, but heavily sweating due to physical exertion. Despite his intimidated aura he wagged his finger triumphantly. "Your spell doesn't affect 'Old Souls', does it? And this is the elixir for turning into an 'Old Soul'. That's what you said."
"You tricked us!" an older boy shouted, putting his foot forward and curling his hands into fists. "He said-"
"I know." the first girl interrupted. Contrary to their appearances she held some authority over him. She maintained an unblinking gaze on the elixir thief. "You can not escape justice for your crimes."
"That's exactly what I'm going to do." He wiped the sweat off his forehead, disguising it as adjusting his hair. "When did alien invaders get so obsessed with justice anyway?" He quickly and nervously fumbled the flask open, keeping an eye on his enemies for the chance of a surprise attack at this critical moment. Then he greedily gulped the liquid down.
"I got the better of you body snatcher freaks." He spread his arms and threw the container aside in a theatrical and environmentally irresponsible manner.
Most of the supposed freaks where dumbfounded by shock and anger. But their leader gave a little smile. "Since you went so far to obtain our secrets, you should have done a bit more research."
The thief lost all expression in his face. "Are you bluffing me?"
"It is true that the flames will not respond to the sins of reincarnated individuals, I designed them that way as I and my comrades have had to stain our hands with sin purging the worlds of man from evil."
"So, then-"
"It is also true that the elixir of eternity, that you tricked my associate into brewing, which is intended only for individuals aligned with the cause of justice, will grant the drinker the gift of reincarnation."
Her enemy swallowed. He had already seen the loophole.
"But you have not yet reincarnated. The elixir will make you an Old Soul, but only after your death. Then, our master, the goddess will decide over your sorry fate. In this life, we shall judge you."
All allies of justice had come forward and were pointing their fingers at him. Then they began saying their memorized lines, one after the other.
"As is our mission, given by the goddess-"
"- we pass judgement on this evildoer."
"For your lies, bribery and betrayal-"
"we will cleanse you from this world."
"Every sin a flame. Incinerate!"
Given no time to comment on this bizarre performance the man suddenly combusted. Every sin and evil deed commited in the past coming back to him as a spark of cleansing fire. The spell was merciful and did not drag out his suffering. He was burned to a crisp within seconds. The Old Souls congratulated themselves on another succesful enactment of vigilante justice. Next time, they wouldn't attract so much eye witnesses.